Gmail SMTP error codes and troubleshooting
Look up Gmail bounce codes, compare message variants and find the next troubleshooting step.
Use the complete SMTP response to identify the next check. A numeric code can describe several different problems, so compare the explanation with the message text before making a change.
This reference groups equivalent messages from Google's published list into practical troubleshooting entries. The meanings are paraphrased; the checks and ownership suggestions are SendPoint's guidance. Open Google's official SMTP error reference.
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Search the published entries by error code or topic.
69 troubleshooting entries.
No matching entry with these filters. Clear the filters, check the complete response, or consult Google's current reference. An unlisted code should not be assigned a meaning by guesswork.
450 4.2.1Recipient receiving too quicklyTemporary response
What it means: The destination account is temporarily unable to accept the incoming rate.
First check: Let the sending service apply retry backoff. Check whether several automations are targeting the same recipient at once.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to investigate Gmail delivery errors
Link to this entry450 4.2.1Workspace relay peak limitTemporary response
What it means: The customer has reached a short-term SMTP relay limit.
First check: Check the Workspace relay logs and combined traffic from all devices. Reduce the affected relay traffic and let the queue retry.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry452 4.2.2Recipient storage fullTemporary response
What it means: The receiving account has no available storage for this delivery.
First check: Preserve the temporary response and use the ESP's retry policy. For essential messages, offer an existing alternative contact route.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to handle Gmail mailbox-full bounces
Link to this entry451 4.3.0 421 4.3.0 421 4.4.5Temporary server problemTemporary response
What it means: The receiving service is temporarily unavailable, busy or declining the transaction.
First check: Allow scheduled retries. If failures persist, give the provider timestamps and connection logs rather than repeatedly resubmitting the campaign.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry451 4.3.0Several destination domains in one transactionTemporary response
What it means: The server refuses the way recipients from different destination domains were grouped.
First check: Ask the mail-server operator to separate recipients by destination domain and check the transaction sequence.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry451 4.4.2Connection timeoutTemporary response
What it means: The SMTP session ended after a timeout.
First check: Inspect network latency, connection reuse and the point at which the session stalled. Let the provider retry through its normal queue.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry451 4.5.0SMTP protocol violationTemporary response
What it means: The conversation between the mail client and server did not follow the expected protocol.
First check: Capture the SMTP command sequence without credentials. Ask the sending software owner to fix the command flow.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry452 4.5.3Too many recipients in a transactionTemporary response
What it means: The recipient count exceeds what the server accepts in this transaction.
First check: Reduce the recipient batch size at the sending server. Keep campaign volume limits separate from the per-transaction limit.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry452 4.5.3Domain policy transaction limitTemporary response
What it means: A policy constraint prevents this recipient from being processed in the current transaction.
First check: Try the affected recipient in a separate transaction through the normal sending queue. Ask the Workspace administrator to inspect the policy if the error repeats.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry421 4.7.0Expired or temporarily closed connectionTemporary response
What it means: The server asks the client to reconnect or retry later.
First check: Use a fresh SMTP session with backoff. Check whether the same command repeatedly triggers the failure before changing message content.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry421 4.7.0Sending IP absent from an allowlistTemporary response
What it means: A recipient-domain policy does not allow the connecting IP.
First check: Give the recipient's Workspace administrator the connecting IP and full response. Ask them to review the intended allowlist policy.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry421 4.7.0 451 4.7.23 550 5.7.25PTR or forward DNS mismatchTemporary and permanent variants
What it means: The connecting IP lacks usable reverse DNS, or the returned hostname does not resolve back to that IP.
First check: Check PTR for the actual sending IP, then its hostname's A or AAAA answer. Ask the IP provider and DNS owner to correct the failing direction.
Who can act: Sending infrastructure provider and DNS administrator.
How to fix Gmail 550 5.7.25 PTR errors
Link to this entry454 4.7.0Too many login attemptsTemporary response
What it means: Authentication attempts have triggered a temporary restriction.
First check: Stop the repeated login loop. Check stored credentials and client configuration before allowing controlled attempts again.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry454 4.7.0Temporary authentication service problemTemporary response
What it means: The server cannot complete login authentication because of a temporary service problem.
First check: Let the client back off. Preserve the response and check whether the error is widespread before rotating otherwise working credentials.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry421 4.7.0 421 4.7.29 550 5.7.29TLS missing or required by recipient policyTemporary and permanent variants
What it means: The SMTP connection does not meet the receiving server's encryption requirement.
First check: Ask the sending provider to verify STARTTLS negotiation on the actual route. Check relay or gateway settings that might disable encryption.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry421 4.7.0 550 5.7.1Low sending IP reputationTemporary and permanent variants
What it means: The response explicitly identifies the reputation of the connecting IP as a concern.
First check: Compare affected IPs, audience sources, complaints and recent volume changes. Ask the ESP about shared-pool issues when relevant.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.0 550 5.7.1Low sending domain reputationTemporary and permanent variants
What it means: The response identifies the sending domain's reputation as a concern.
First check: Review sending streams associated with that domain, subscription expectations and complaint patterns. Correct the responsible stream before increasing traffic.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.0Suspicious message content or linksTemporary response
What it means: The response points to the message or its linked destinations.
First check: Review a real message and the destinations behind its links. Check for compromised pages, misleading content or unexpected redirects and correct confirmed issues.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry451 4.7.24 550 5.7.24Suspicious SPF entriesTemporary and permanent variants
What it means: Google flags entries in the SPF policy as suspicious.
First check: Inventory authorized senders and review the policy with the DNS owner. The code alone does not identify the offending entry; preserve the full response for the provider.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry451 4.7.26Authentication blocked by temporary DNS failureTemporary response
What it means: DMARC-related authentication cannot complete because DNS lookups are failing temporarily.
First check: Check authoritative DNS availability for SPF, DKIM and DMARC. Repair the DNS issue and let the sending queue retry; do not weaken DMARC as the default response.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry421 4.7.26 550 5.7.26Message lacks passing authenticationTemporary and permanent variants
What it means: The error reports that neither the checked SPF nor DKIM result passed.
First check: Inspect the envelope domain, sending IP, DKIM selector and signature from that workflow. Correct the responsible sender and verify a fresh message.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry550 5.7.26SPF hard-fail policy rejected the senderPermanent response
What it means: The envelope sender domain publishes -all, and the connecting IP did not pass SPF.
First check: Check whether this route is authorized for the envelope domain. Repair the sender configuration or SPF inventory rather than changing -all blindly.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry550 5.7.26DMARC policy rejectionPermanent response
What it means: The message does not satisfy the visible From domain's DMARC policy.
First check: Check passing SPF or DKIM and alignment with the From domain. A passing signature from an unrelated provider domain may not establish alignment.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry421 4.7.27 550 5.7.27SPF did not passTemporary and permanent variants
What it means: The message failed the SPF requirement described in the response.
First check: Inspect the envelope identity and actual connecting IP. Check the relevant SPF policy, authorized route and DNS evaluation errors.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry421 4.7.28Unusual sending rateTemporary response
What it means: Gmail is restricting traffic after detecting an unusual sending pattern.
First check: Compare the first failure with campaign schedules and queue changes. Reduce the affected stream, investigate its audience and coordinate retry pacing with the ESP.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.28 550 5.7.28Sending IP or netblock restrictedTemporary and permanent variants
What it means: The response names an IP address or IP netblock associated with unusual or unwanted traffic.
First check: Group errors by the named IP or netblock. Ask the infrastructure owner to inspect traffic across that scope, including other senders on shared infrastructure.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.28DKIM domain restrictedTemporary response
What it means: The response names the DKIM signing domain as the affected identity.
First check: Group sending streams by their DKIM d= domain. Review complaints and acquisition sources for those streams before expanding sending.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.28SPF domain restrictedTemporary response
What it means: The response names the SPF-authenticated domain as the affected identity.
First check: Group messages by envelope sender domain. Check which applications share it and correlate restrictions with their sending schedules.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.28URL domain restrictedTemporary response
What it means: The restriction concerns a domain used in message links.
First check: Inventory linked and tracking domains in affected messages. Ask the provider to investigate the named destination and repair any confirmed misuse.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry421 4.7.28Repeated Message-ID quotaTemporary response
What it means: The response says too many messages used the same Message-ID.
First check: Check message generation, replay and forwarding for repeated identifiers. Fix duplicated generation without treating ordinary SMTP retries as new messages by default.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry421 4.7.30 550 5.7.30DKIM did not passTemporary and permanent variants
What it means: The message failed the DKIM requirement described in the response.
First check: Check the signing selector, DNS public key and signature. Compare the message before and after intermediate systems that might alter signed content.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry421 4.7.40 550 5.7.40DMARC record or policy missingTemporary and permanent variants
What it means: The sending domain lacks a usable DMARC record with a policy.
First check: Check the correct _dmarc DNS name and record syntax. Verify legitimate senders before introducing a more restrictive policy.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry421 4.7.32 421 5.7.32From domain alignment failureMixed code classes: check full reply
What it means: The visible From domain does not align with a passing SPF or DKIM identity. Google lists both code combinations, including the mixed-class 421 5.7.32 entry.
First check: Check the full reply and the ESP's handling of the mixed-class entry. Compare From, envelope sender and DKIM signing domains under the published alignment policy.
Who can act: Sending platform and domain DNS administrator.
How to check SPF, DKIM and DMARC for Gmail
Link to this entry550 5.1.1Recipient address does not existPermanent response
What it means: The receiving system cannot find the requested mailbox.
First check: Check for a transcription error against the recipient's own details. Honor the ESP's invalid-address suppression; do not keep resending to the same address.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to investigate Gmail delivery errors
Link to this entry553 5.1.2Recipient domain not foundPermanent response
What it means: The domain part of the recipient address cannot be resolved as expected.
First check: Check spelling, trailing punctuation and the destination domain's DNS. Correct only a verified error rather than guessing a replacement address.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to investigate Gmail delivery errors
Link to this entry553 5.1.3Invalid recipient address syntaxPermanent response
What it means: The SMTP recipient address is malformed.
First check: Inspect the exact RCPT TO value produced by the application. Remove formatting defects and verify the intended address with its owner when necessary.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to investigate Gmail delivery errors
Link to this entry553 5.1.7Invalid sender address syntaxPermanent response
What it means: The SMTP sender address is malformed.
First check: Inspect the envelope sender generated by the sending application. Repair address construction and test the same workflow again.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry550 5.2.1Recipient account inactivePermanent response
What it means: The response identifies an inactive destination account.
First check: Preserve the failure reason and honor the platform's suppression. Use a known alternative contact route for essential information.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to investigate Gmail delivery errors
Link to this entry550 5.2.1Recipient receiving-rate limit, permanent replyPermanent response
What it means: The account cannot receive at the current rate, but this particular response uses a 5xx rejection.
First check: Treat this transaction as failed. Follow the ESP's handling rather than forcing retries simply because the underlying rate condition may later change.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to investigate Gmail delivery errors
Link to this entry552 5.2.2Storage full and account inactivePermanent response
What it means: The response combines an unavailable storage condition with inactivity.
First check: Retain both details when reviewing the contact. Use the provider's supported suppression-review process if the recipient later resolves the issue and requests mail.
Who can act: Recipient or recipient administrator; sender manages contact handling.
How to handle Gmail mailbox-full bounces
Link to this entry552 5.3.4Message size or attachment count limitPermanent response
What it means: The message exceeds a size or attachment-count limit specified by the receiver.
First check: Check the actual encoded message size and attachment count. Reduce the message appropriately and review the limit named in the response.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry552 5.3.4Header size, count or field limitPermanent response
What it means: The message exceeds a limit on total headers, a header field, a header name or the Subject field.
First check: Inspect the exact field and limit in the response. Check for duplicated headers or excessive tracking data and fix the message builder.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry550 5.4.5 550 5.7.1Daily account or SMTP relay quotaPermanent response
What it means: The response names a daily user or customer relay sending limit.
First check: Review combined traffic from clients and devices. Queue legitimate pending mail within the service's limits and investigate unexpected traffic.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry554 5.4.6Routing loop or too many hopsPermanent response
What it means: The message passed through more than 50 relay hops, suggesting a routing loop.
First check: Trace Received headers and forwarding rules. Remove circular routing between mailboxes, gateways or support systems before sending a fresh message.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry503 5.5.1SMTP commands out of sequencePermanent response
What it means: The server received commands in an invalid order. Variants mention EHLO/HELO, RCPT, or DATA following BDAT.
First check: Inspect the command transcript and fix the client's SMTP state handling. Ask the provider to reproduce the specific sequence.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry502 5.5.1Unknown or unsupported SMTP commandPermanent response
What it means: The server does not recognize or implement a command; repeated invalid commands may close the session.
First check: Check advertised server capabilities and the protocol or port configured in the client. Remove unsupported command use.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry501 5.5.2 555 5.5.2SMTP syntax or decoding errorPermanent response
What it means: A command or response has invalid syntax or cannot be decoded.
First check: Capture the failing command without passwords or tokens. Fix escaping, line endings or argument construction in the sending client.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry550 5.5.3Sender recipient limitPermanent response
What it means: The sender has supplied more recipients than the server permits.
First check: Review recipient batching and the applicable sending limit with the provider. Do not treat this as proof that the recipient addresses are invalid.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry501 5.5.4Invalid or empty HELO/EHLO argumentPermanent response
What it means: The client did not identify itself with an acceptable HELO or EHLO argument.
First check: Configure the mail client's intended hostname and inspect the actual greeting sent over the connection.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry554 5.6.0Malformed email messagePermanent response
What it means: The message itself does not meet the required email format.
First check: Inspect the raw message with the sending platform. Repair malformed headers or body structure and test the original workflow.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry552 5.7.0Content or attachment security blockPermanent response
What it means: The message content or attachment is blocked as a potential security issue.
First check: Review attachment types and the actual file contents with the sender. Use an appropriate approved sharing method instead of disguising a blocked file.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry503 5.7.0Identity changed within the SMTP sessionPermanent response
What it means: The client attempted an identity change the server does not permit.
First check: Inspect connection pooling and authentication state. Keep account identities separated in properly initialized sessions.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry550 5.7.0 550 5.7.1Workspace relay identity or authorization mismatchPermanent response
What it means: The sending IP, domain or credentials do not match the intended Workspace relay configuration.
First check: Have the administrator verify registered sending IPs, domain membership and SMTP AUTH or HELO/EHLO identification for the actual route.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry550 5.7.0Relay sending denied or account suspendedPermanent response
What it means: The relay refuses sending; some variants identify a suspension related to abuse.
First check: Read the complete response and review the affected account in Workspace. Investigate unexpected sending and resolve the account restriction through the administrator.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry554 5.7.0 530 5.7.0SMTP login authentication requiredPermanent response
What it means: The client must authenticate before issuing further commands, or has issued too many unauthenticated commands.
First check: Configure the provider-supported login method. Distinguish account login authentication from SPF, DKIM and DMARC on outgoing messages.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry530 5.7.0STARTTLS must happen firstPermanent response
What it means: The client tried to continue before starting the required encrypted connection.
First check: Enable STARTTLS on the correct submission route and confirm the client negotiates it before the relevant commands.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry550 5.7.1Workspace or domain policy rejectionPermanent response
What it means: A sender or recipient policy prohibits the message. The gcdp marker identifies a custom Workspace policy.
First check: Ask the relevant administrator to inspect the named policy and a representative rejected message. A campaign rewrite may not address an administrative rule.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry550 5.7.1Message classified as unsolicitedPermanent response
What it means: The reply identifies the message as likely unwanted email.
First check: Review permission, acquisition source, frequency and the content recipients expected. Check the affected stream before attempting another campaign.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry550 5.7.1IPv6 sender requirementsPermanent response
What it means: The reply identifies IPv6 PTR or authentication requirements.
First check: Inspect reverse and forward DNS for the actual IPv6 address and verify message authentication on that route.
Who can act: Sending infrastructure provider and DNS administrator.
How to fix Gmail 550 5.7.25 PTR errors
Link to this entry550 5.7.1Missing or invalid From or Message-IDPermanent response
What it means: A required From or Message-ID field is absent or invalid; From may contain an invalid domain or multiple addresses.
First check: Inspect the raw headers generated by the application. Correct the named field and test a newly generated message.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry550 5.7.1Duplicate, malformed or improperly encoded headersPermanent response
What it means: A header violates formatting rules, including duplicates, disallowed Unicode or encoded-word syntax in the named field.
First check: Identify the field from the full response. Check whether a gateway and application both add it, then repair its generation or encoding.
Who can act: Sending application or ESP technical team.
How to investigate Gmail delivery errors
Link to this entry550 5.7.1Sending rate restricted, permanent replyPermanent response
What it means: The reply describes rate limiting but rejects this transaction with a 5xx code.
First check: Stop repeated manual submissions. Review volume and the provider's rejection handling before scheduling further traffic.
Who can act: Email program owner and ESP deliverability team.
How to recover after Gmail complaints or throttling
Link to this entry550 5.7.1IP not authorized for direct deliveryPermanent response
What it means: The connecting IP is not permitted to deliver directly to Google's servers.
First check: Configure the authorized SMTP relay recommended by the sending service. Confirm the intended route with the infrastructure owner.
Who can act: Sending infrastructure provider and DNS administrator.
How to investigate Gmail delivery errors
Link to this entry523 5.7.10Commands pipelined after STARTTLSPermanent response
What it means: The client sent commands at a point where the server forbids pipelining around STARTTLS.
First check: Have the mail software owner inspect its TLS state transition and command buffering. Correct the protocol implementation.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry501 5.7.11Unexpected command parametersPermanent response
What it means: A command was supplied with parameters where none are accepted.
First check: Inspect the failing command and remove invalid arguments in the client configuration or implementation.
Who can act: Mail-server, application or network operator.
How to investigate Gmail delivery errors
Link to this entry534 5.7.14 534 5.7.90Browser sign-in requiredPermanent response
What it means: The account must complete a browser sign-in or account check before the client can proceed.
First check: Have the account owner sign in through Google's normal interface and review the account state. Never paste credentials into a bounce lookup.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry504 5.7.40Unsupported login authentication methodPermanent response
What it means: The client requested an unrecognized authentication mechanism; a variant names obsolete XOAUTH.
First check: Update the client to a currently supported authentication mechanism. This 504 response is distinct from 550 5.7.40 about DMARC.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry535 5.7.80Login credentials rejectedPermanent response
What it means: The SMTP login attempt was rejected.
First check: Verify the account, supported login method and administrator restrictions. Check for stale client credentials without sharing passwords or tokens in support logs.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entry534 5.7.90App password requiredPermanent response
What it means: The response requests an application-specific password for this account and client.
First check: Check whether app passwords are permitted for the account and whether the client supports a preferred modern sign-in method. Follow the account administrator's configuration.
Who can act: Google Workspace administrator or account owner.
How to investigate Gmail delivery errors
Link to this entryRead the response before choosing a fix
A 4xx response generally leaves the sending system an opportunity to retry later. A 5xx response rejects the request and should not trigger repeated unchanged submissions. Neither response class, by itself, proves that the recipient address is invalid.
Check the three-digit SMTP reply, the enhanced status code and the text together. Google's list includes 421 5.7.32, whose classes differ. This reference preserves the documented combination and flags it for review; confirm the actual wire response and your ESP's handling.
The gsmtp marker identifies Google's SMTP service. The gcdp marker points to a custom Google Workspace policy. When a custom policy is named, involve the relevant administrator.
Collect useful evidence
Record the complete response, timestamp and timezone, sending IP, envelope domain, visible From domain and affected workflow. For delivery failures, compare more than one example to see whether a single route or a wider stream is affected.
Keep login passwords, access tokens and unnecessary recipient information out of support examples. Fix the identified cause and verify a fresh controlled message before calling the issue resolved.
Related guides
- How to investigate Gmail delivery errors
- How to fix Gmail 550 5.7.25 PTR errors
- How to check SPF, DKIM and DMARC for Gmail
- How to handle Gmail mailbox-full bounces
Sources and scope
Based on the supplied Google SMTP reference and checked against the online reference on 20 September 2026. Covers its 57 distinct code pairs in 69 grouped troubleshooting entries, including sending-to-Gmail errors and Google Workspace submission or relay errors. Google's wording and available codes can change.