| Error Code |
Meaning |
Troubleshooting |
Glossary |
| 421, "4.3.0" |
Temporary System Problem. Try again later |
Retry sending the message later |
SMTP: Simple Mail Transfer Protocol, a protocol for sending e-mail messages |
| 421, "4.4.5" |
The server is busy; try again later |
Retry sending the message later |
- |
| 421, "4.7.0" |
IP not in whitelist for RCPT domain, closing connection |
Check if your IP address is allowed to send emails to the receiver |
RCPT: SMTP command to specify the recipient of the message |
| 421, "4.7.0" |
Our system has detected an unusual rate of unsolicited mail originating from your IP address. |
Review your sent emails for any potential unsolicited mail. |
- |
| 421, "4.7.0" |
Temporary System Problem. Try again later |
Retry sending the message later |
- |
| 421, "4.7.0" |
TLS required for RCPT domain, closing connection |
Make sure your system supports TLS (Transport Layer Security) |
TLS: Protocol that provides communications security over a computer network |
| 421, "4.7.0" |
Try again later, closing the connection |
Retry sending the message later |
DoS: Denial of Service, a cyber-attack that makes a machine or network resource unavailable |
| 450, "4.2.1" |
The user you are trying to contact is receiving mail too quickly |
Resend your message at a later time |
- |
| 450, "4.2.1" |
The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered. |
Resend your message at a later time. |
- |
| 450, "4.2.1" |
Peak SMTP relay limit exceeded for customer |
Try reducing the number of sent emails |
SMTP relay: Process of transferring an email from one mail server to another |
| 451, "4.3.0" |
The mailMail server temporarily rejected the message |
Retry sending the message later |
- |
| 451, "4.3.0" |
Multiple destination domains per transaction is unsupported |
Send your message to a single domain at a time |
Domain: Part of the network address that represents a specific entity (like a company) on the internet |
| 451, "4.4.2" |
Timeout - closing connection |
Retry sending the message later |
- |
| 451, "4.5.0" |
SMTP protocol violation |
Ensure that your system is correctly following the SMTP protocol |
SMTP: Simple Mail Transfer Protocol, a protocol for sending e-mail messages |
| 452, "4.2.2" |
The email account that you tried to reach is over quota |
Ask the recipient to clear their inbox |
Over quota: When a user has filled their storage limit |
| 452, "4.5.3" |
Domain policy size per transaction exceeded |
Try sending to the recipient in a separate transaction |
- |
| 452, "4.5.3" |
Your message has too many recipients |
Reduce the number of recipients for your message |
- |
| 454, "4.5.0" |
SMTP protocol violation, no commands allowed to pipeline after STARTTLS. |
Check your SMTP relay settings and try again. |
STARTTLS: A way to take an existing insecure connection and upgrade it to a secure connection using SSL/TLS. |
| 454, "4.7.0" |
Cannot authenticate due to a temporary system problem. |
Try again later. If the problem persists, contact your email provider. |
Authenticate: To verify the identity of a user, device, or system. |
| 501, "5.5.2" |
Cannot decode the response. |
This can be a server-side issue. Try again later or contact your service provider. |
Decode: To convert from an encoded or encrypted form to plain text. |
| 501, "5.5.4" |
HELO/EHLO argument is invalid. |
Check your SMTP server configuration for errors. |
HELO/EHLO: SMTP commands sent by an email server to identify itself when connecting to another email server. |
| 502, "5.5.1" |
Too many unrecognized commands, goodbye. |
Check your SMTP commands for any mistakes. |
SMTP Commands: Instructions that an email client communicates to the mail server to send an email. |
| 502, "5.5.1" |
Unimplemented command. |
Ensure that your email client is using commands recognized by the SMTP server. |
Unimplemented: Not yet put into effect. |
| 503, "5.5.1" |
"EHLO/HELO first. |
Your email client may be out of order. Ensure it starts with an EHLO or HELO command. |
EHLO/HELO: Commands used by SMTP to initiate the connection. |
| 503, "5.5.1" |
MAIL first. |
The MAIL command needs to be the first command in your SMTP conversation. |
MAIL: An SMTP command is used to initiate mail transfer. |
| 503, "5.5.1" |
RCPT first. |
The RCPT command needs to be the first command in your SMTP conversation. |
RCPT: An SMTP command is used to identify the email's recipient. |
| 503, "5.7.0" |
No identity changes are permitted. |
Check your SMTP configuration or contact your service provider. |
Identity: The unique identifier (often a username or email address) associated with a specific user. |
| 504, "5.7.4" |
Unrecognized Authentication Type |
Check your SMTP settings and ensure you're using a supported authentication type. |
Authentication Type: The method used to verify a user's identity, such as password or OAuth. |
| 530, "5.5.1" |
Authentication Required |
Check that you're properly authenticated with your SMTP credentials. |
Authentication: The process of verifying a user's identity. |
| 530, "5.7.0" |
Must issue a STARTTLS command first |
Ensure that your email client initiates the SMTP connection with a STARTTLS command. |
STARTTLS: A way to take an existing insecure connection and upgrade it to a secure connection using SSL/TLS. |
| 535, "5.5.4" |
Optional Argument not permitted for that AUTH mode |
Check your SMTP settings, especially the AUTH command and its arguments. |
AUTH: An SMTP command is used to authenticate the client to the server. |
| 535, "5.7.1" |
Application-specific password required |
Use an application-specific password if you have 2-Step Verification enabled. |
Application-specific password: A password for applications not supporting logging in using 2-Step Verification. |
| 535, "5.7.1" |
Please log in with your web browser and then try again |
Log into your account via your web browser, then resend your email. |
- |
| 535, "5.7.1" |
Username and Password not accepted |
Ensure that you're entering the correct username and password. If you're using 2-Step Verification, use an application-specific password. |
- |
| 550, "5.1.1" |
The email account that you tried to reach does not exist |
Check the recipient's email address for typos or unnecessary spaces. |
- |
| 550, "5.2.1" |
The email account that you tried to reach is disabled |
You cannot send an email to a disabled account. Contact the recipient through other means if possible. |
- |
| 550, "5.2.1" |
The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered |
Try again later. |
- |
| 550, "5.4.5" |
Daily sending quota exceeded |
Limit the number of emails you send each day or upgrade your Google Workspace edition if you need to send more mail. |
Quota: A set limit on how much of a particular resource a user or program can use. |
| 550, "5.4.5" |
Daily SMTP relay limit exceeded for user |
Check your SMTP relay settings or upgrade your Google Workspace edition to send more mail. |
SMTP relay: A service used to send large volumes of email. |
| 550, "5.7.0" |
Mail relay denied |
The email was not sent because the SMTP relay was denied; contact your service provider. |
Relay: The act of passing email from one server to another. |
| 550, "5.7.0" |
Mail Sending denied |
Ensure the sender account is active and part of your Google Workspace domain. |
- |
| 550, "5.7.1" |
Email quota exceeded |
You'll need to free up storage space or purchase more in order to send additional emails. |
Quota: A set limit on how much of a particular resource a user or program can use. |
| 550, "5.7.1" |
Invalid credentials for relay |
Check the configuration of your SMTP relay service. |
Credentials: Information that includes identification and proof of identification used to gain access to resources. |
| 550, "5.7.1" |
Our system has detected an unusual rate of unsolicited mail originating from your IP address. |
If you're not sending spam, examine your network for malware or misconfigured software. |
Unsolicited mail: Email that a user did not ask for (usually refers to spam). |
| 550, "5.7.1" |
Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail, this message has been blocked |
Ensure the email complies with Gmail’s Bulk Email Senders Guidelines |
Unsolicited mail: Email that a user did not ask for (usually refers to spam). |
| 550, "5.7.1" |
The IP you're using to send mail is not authorized to send email directly to our servers |
Use the SMTP relay at your service provider instead |
SMTP relay: A service used to send large volumes of email. |
| 550, "5.7.1" |
The user or domain that you are sending to (or from) has a policy that prohibits the mail that you sent |
Review the email content and contact the domain administrator for further details. |
Policy: A rule or set of rules governing how systems or organizations operate. |
| 550, "5.7.1" |
Unauthenticated email is not accepted from this domain |
Check your SMTP settings and ensure the email passes SPF or DKIM authentication |
Unauthenticated email: An email that hasn't passed validation checks to prove it came from the domain it claims to be from. |
| 550, "5.7.1" |
Daily SMTP relay limit exceeded for customer |
Check your SMTP relay settings or upgrade your Google Workspace edition if you need to send more mail |
SMTP relay: A service used to send large volumes of email. |
| 550, "5.7.26" |
Unauthenticated email from domain name is not accepted due to domain's DMARC policy. |
Adjust your DMARC records, consider using a service like Google Workspace to send your mail, and contact the administrator of the receiving mail server. |
DMARC: An email validation system that detects and prevents email spoofing. |
| 550, "5.7.26" |
This message does not have authentication information or fails to pass authentication checks. |
Ensure the email passes SPF or DKIM authentication |
Authentication: The process of verifying the identity of a user, process, or device. |
| 550, "5.7.26" |
This message fails to pass SPF checks for an SPF record with a hard fail policy. |
Adjust your SPF records and ensure the email passes SPF authentication |
SPF (Sender Policy Framework): An email authentication method designed to detect forging sender addresses during email delivery. |
| 552, "5.2.2" |
The email account that you tried to reach is over quota |
Ask the recipient to clear some space in their inbox |
Quota: A set limit on how much of a particular resource a user or program can use. |
| 552, "5.2.3" |
Your message exceeded Google's message size limits |
Reduce the size of the message and try again |
- |
| 553, "5.1.2" |
We weren't able to find the recipient domain |
Double-check the recipient's email address for typos or unnecessary spaces |
Domain: The part of an email address that comes after the @ symbol. |
| 554, "5.6.0" |
The mail message is malformed. Not accepted |
Check the format of your email and try again |
Malformed: Structured incorrectly or in a way that does not conform to the expected format. |
| 554, "5.6.0" |
Message exceeded 50 hops; this may indicate a mail loop |
Check your SMTP settings to prevent potential mail loops |
Mail Loop: A situation in which an email message is continually bounced back and forth between two or more servers. |
| 554, "5.7.0" |
This message was blocked because its content presents a potential security issue. |
Ensure the content and attachments of the email comply with Google’s policies. |
- |
| 554, "5.7.0" |
IP has been blacklisted due to spam activity |
Contact your service provider and take steps to remove your IP from the blacklist. |
Blacklist: A list of entities blocked or denied access to a certain system or protocol. |
| 554, "5.7.1" |
The transaction failed because the recipient's mailbox is full |
Ask the recipient to clear some space in their mailbox |
Mailbox: An electronic folder where incoming emails are stored for a user. |
| 554, "5.7.1" |
The message you're trying to send exceeds the recipient's size limits |
Reduce the size of the message or contact the recipient to increase their size limits |
Size limits: Restrictions on the maximum size of an email message or attachment. |
| 555, "5.5.2" |
Syntax error |
Check the syntax of the email addresses, commands, or configuration settings. |
Syntax: The set of rules that dictate the structure and format of a language or code. |
| 555, "5.5.4" |
Optional Argument not permitted for that AUTH mode |
Review your SMTP authentication settings and ensure they are correctly configured |
Authentication: The process of verifying the identity of a user, process, or device. |
| 555, "5.7.1" |
Authentication required for relay |
Provide valid authentication credentials for the SMTP relay |
Relay: Forwarding email messages from one mail server to another. |
| 555, "5.7.1" |
Please log in with your web browser and then try again |
Access your Gmail account via a web browser and follow any on-screen prompts to resolve the issue |
Web browser: A software application used to access and view websites. |
| 555, "5.7.1" |
Username and Password not accepted |
Verify the correctness of your username and password, and ensure they are correctly entered. |
Username: A unique identifier used to access a system or service. |
| 550, "5.1.1" |
The email account that you tried to reach does not exist |
Double-check the recipient's email address for typos, or contact the recipient to confirm the correct email address |
Typos: Errors or mistakes in the spelling or formatting of text. |
| 550, "5.2.1" |
The email account that you tried to reach is disabled |
Verify the status of the recipient's email account or contact the recipient to confirm the account status |
Disabled: Inactive or deactivated. |
| 550, "5.4.5" |
Daily sending quota exceeded |
Reduce the number of outgoing emails or upgrade your Google Workspace edition for higher sending quotas. |
I am sending quota: The maximum number of emails allowed to be sent within a specified time period. |
| 550, "5.4.5" |
Daily SMTP relay limit exceeded for user |
Check your SMTP relay sending limits or contact your administrator for assistance |
SMTP relay: A service used to send large volumes of email. |
| 550, "5.7.0" |
Mail relay denied |
Check your SMTP relay settings and ensure they comply with Google's policies. |
Mail relay: Forwarding email messages from one mail server to another. |
| 550, "5.7.0" |
Mail Sending denied. This error occurs if the sender account is disabled or not registered within your Google Workspace domain. |
Verify the sender's email account status and ensure it is enabled and registered within the Google Workspace domain. |
Domain: A group of computers or devices that share a common set of rules and settings. |
| 550, "5.7.1" |
Email quota exceeded |
Reduce your mailbox size or upgrade your Google Workspace edition for higher storage quotas. |
Quota: The allocated amount or limit for a particular resource or service. |
| 550, "5.7.1" |
Invalid credentials for relay |
Verify the correctness of your authentication credentials for the SMTP relay. |
Credentials: Information used to verify one's identity or access a system. |
| 550, "5.7.1" |
Our system has detected an unusual rate of unsolicited mail originating from your IP address. |
Check your network for malware or misconfigured software to prevent spamming activities. |
Unsolicited mail: Email that is sent without the recipient's explicit consent. |
| 550, "5.7.1" |
Our system has detected that this message is likely unsolicited mail |
Ensure your email content and attachments comply with Google's spam policies to prevent message blocking |
Spam: Unsolicited or unwanted email, often sent in bulk. |
| 550, "5.7.1" |
The IP you're using to send mail is not authorized to send emails directly to our servers. |
Use the SMTP relay provided by your service provider to send an email or contact Google support for further assistance |
SMTP: Simple Mail Transfer Protocol, the standard protocol used for email transmission. |
| 550, "5.7.1" |
The user or domain that you are sending to (or from) has a policy that prohibits the mail that you sent |
Review and comply with the policies of the recipient's user or domain to ensure successful email delivery. |
Policies: Rules or guidelines that govern the behavior or actions within a system or organization. |
| 550, "5.7.1" |
Unauthenticated email is not accepted from this domain |
Configure your email client or server to authenticate before sending emails |
Authentication: The process of verifying the identity or legitimacy of a user or entity. |
| 550, "5.7.1" |
Daily SMTP relay limit exceeded for customer |
Review your SMTP relay sending limits or contact your administrator for assistance. |
SMTP relay: A service used to send large volumes of email. |
| 550, "5.7.26" |
Unauthenticated email from domain name is not accepted due to domain's DMARC policy |
Authenticate your email with the appropriate mechanisms specified by the DMARC policy of the recipient's domain. |
DMARC: Domain-based Message Authentication, Reporting, and Conformance, a security protocol for preventing email spoofing. |
| 550, "5.7.26" |
This message does not have authentication information or fails to pass authentication checks (SPF or DKIM) |
Ensure your email passes SPF and DKIM authentication checks to improve deliverability. |
SPF: Sender Policy Framework, a protocol that validates the origin of email messages. DKIM: DomainKeys Identified Mail, a method for validating the authenticity of email messages. |
| 552, "5.2.2" |
The email account that you tried to reach is over quota |
Advise the recipient to free up space in their mailbox by deleting unnecessary emails |
Quota: The allocated storage capacity for an email account. |
| 552, "5.2.3" |
Your message exceeded Google's message size limits |
Reduce the size of your email message or use alternative methods for sharing large files |
Message size limits: The maximum allowed size for an email message, including attachments. |
| 553, "5.1.2" |
We weren't able to find the recipient domain |
Verify the correctness of the recipient's email address and check for any typos or formatting errors. |
Domain: The part of an email address after the "@" symbol indicating the recipient's email server. |
| 554, "5.6.0" |
The mail message is malformed. Not accepted |
Review the structure and content of your email message for any errors or inconsistencies. |
Malformed: Incorrectly structured or formatted. |
| 554, "5.6.0" |
Message exceeded 50 hops; this may indicate a mail loop |
Investigate and resolve any circular forwarding or routing configurations causing the mail loop |
Mail loop: A situation where an email is continuously forwarded or routed between multiple recipients. |
| 554, "5.7.0" |
Too Many Unauthenticated commands |
Review your SMTP authentication settings and ensure proper authentication during the SMTP session. |
Unauthenticated commands: SMTP commands are issued without proper authentication. |
| 555, "5.5.2" |
Syntax error |
Double-check the syntax and format of email addresses, commands, or configuration settings. |
Syntax: The rules and structure that govern the correct arrangement of elements in a language or code. |
