SMTP relay service error messages

• Email is being sent from a domain or IP that isn't registered in Google Workspace. Please sign in to your Google Workspace account and verify that your sending device IP is registered within Google Workspace SMTP relay service settings. See SMTP Relay service setting for more information.
• The domain with the configured policy couldn't be properly identified. Please ensure that the sending client uses an appropriate value for both the HELO command; ideally, the fully qualified domain name (FQDN) of the sending device, and that the SMTP sender (MAIL FROM:) identifies the send address properly (MAIL FROM: <user@example.com>).

The IP address you registered in the Google Workspace SMTP relay service setting doesn't match the domain of the account this email is being sent from. If you are trying to relay mail from a domain that isn't registered in your Google Workspace account, you must configure your mail server either to use SMTP AUTH to identify the sending domain or to present one of your domain names in the HELO or EHLO command. See SMTP Relay service setting for more information.

The customer has reached their daily SMTP relay limit. See SMTP Relay service setting for SMTP relay sending limits, or contact your administrator for additional help.

This is a temporary error. The customer has exceeded their peak SMTP relay limit, and relay mail for the customer is temporarily being deferred. See SMTP Relay service setting for SMTP relay sending limits.

The user has reached their daily SMTP relay limit. See SMTP Relay service setting for SMTP relay sending limits, or contact your administrator for additional help.

There is a 100-recipient limit per SMTP transaction for smtp-relay.gmail.com. To send messages to additional recipients, start another transaction (new SMTP connection or RSET command).

The message passed through more than 50 mail server hops before reaching its final destination, which usually shows a mail routing loop. To diagnose and resolve the loop:

• Inspect Received: headers to find the loop cycle: Examine the Received: headers in the bounced message or trace the message in Email Log Search to identify which mail servers are repeatedly passing the message back and forth. For details, go to Find messages with Email Log Search.
• Don't route Gmail-originated messages back into smtp-relay.gmail.com: If a message originates from a Google Workspace mailbox, don't route it to a third-party or on-premises gateway that relays the message back through smtp-relay.gmail.com. Doing so creates a mail loop. For details, go to Route outgoing SMTP relay messages through Google.
• Review Admin console Routing and Content compliance rules: In the Google Admin console (Apps Google Workspace Gmail Routing and Compliance), verify that outbound or inbound routing rules that modify the route to an external gateway exclude messages already arriving from that gateway's IP address or hostname.
• Check for circular forwarding and automatic replies: Verify that recipient mailboxes, Google Groups, or aliases don't have automatic forwarding rules or out-of-office replies set up to forward messages back to each other in a cycle.

The server encountered a temporary sign-in problem or restricted repeated sign-in attempts on the connection. To diagnose and resolve this error:

• Reuse open SMTP connections across messages: Don't open a new TCP connection and run AUTH for every message. Keep existing SMTP connections to smtp-relay.gmail.com open (connections can stay open for up to 10 minutes) and send RSET followed by MAIL FROM to send additional messages over the same signed-in session.
• Try again with exponential backoff: Because 454 4.7.0 is a temporary (4xx) error, set up your mail server or sending application to queue the deferred message and try again with exponential backoff instead of immediately trying to sign in again in a loop.
• Verify TLS, IP allowlist, and SMTP AUTH settings: Confirm that your mail server or device connects over TLS (port 587 with STARTTLS or port 465), that your sending public IP addresses are registered in the SMTP relay service setting, and that your EHLO or HELO domain and SMTP AUTH username and password match an active Google Workspace user on your registered domain. For details, go to Route outgoing SMTP relay messages through Google.