5.7.0 Security or policy problem

Gmail

• 552 5.7.0This message was blocked because its content presents a potential security issue.

  The message was blocked because its content or an attachment is a potential security issue.

• 503 5.7.0No identity changes permitted.

  The client tried to change identity within the same session, which Gmail does not allow.

• 550 5.7.0Email relay denied ip-address. Invalid credentials for relay for one of the domains in: domain-name (as obtained from HELO and (E)MAIL FROM). Email is being sent from a domain or IP address which isn't registered in your Workspace account. Please login to your Workspace account and verify that your sending device IP address has been registered within the Workspace SMTP Relay Settings.

  Google Workspace's SMTP relay did not recognise the sender: the IP address or the HELO and MAIL FROM domains do not match the relay's configuration.

• 550 5.7.0Email relay denied ip-address. The sending email account has been temporarily suspended due to abuse.

  The account sending through the SMTP relay was temporarily suspended for abuse.

• 550 5.7.0Email sending denied.

  Sending was denied by Google Workspace's SMTP relay service.

• 554 5.7.0Too many unauthenticated commands.

  The client sent too many commands without authenticating.

• 530 5.7.0Authentication required.

  The server requires authentication before sending.

• 530 5.7.0Must issue a STARTTLS command first.

  The client must start TLS (STARTTLS) before this command (RFC 3207).

• 552 5.7.0This message was blocked because its content presents a potential security issue.

  The message was blocked because its content or an attachment is a potential security issue.

• 421 4.7.0Connection expired, try reconnecting.

  The connection expired; the sending server has to reconnect.

• 421 4.7.0IP not in whitelist for RCPT domain, closing connection.

  The recipient's domain accepts mail only from certain IP addresses, and yours is not among them. Only the recipient's administrator can change that.

• 421 4.7.0Try again later, closing connection.

  Gmail temporarily rejected the message, with no other reason. The sending server's automatic retry usually solves it.

• 421 4.7.0The IP address sending this message does not have a PTR record, or the corresponding forward DNS entry does not point to the sending IP. To protect our users from spam, email sent from your IP address has been temporarily rate limited.

  The sending IP address has no PTR, or the PTR name does not lead back to the same address, so Gmail limits or blocks its mail. The PTR is set by whoever holds the IP address. Check with SMTP server check.

• 454 4.7.0Too many login attempts, please try again later.

  Too many login attempts on the account; wait before trying again.

• 454 4.7.0Cannot authenticate due to a temporary system problem. Try again later.

  Authentication fails because of a temporary problem at Google; try again later.

• 421 4.7.0TLS required for RCPT domain, closing connection.

  The recipient's domain requires TLS and the connection was not encrypted; the sending server must use STARTTLS. Check with Mail delivery test.

• 421 4.7.0This message is suspicious due to the very low reputation of the sending IP address. To protect our users from spam, email sent from your IP address has been temporarily rate limited.

  The sending IP address has a very low reputation at Gmail, so its mail is limited or blocked. Check blocklists, authentication and what you send; Postmaster Tools shows the reputation. Check with Blacklist check.

• 421 4.7.0This message is suspicious due to the very low reputation of the sending domain. To best protect our users from spam, the message has been blocked.

  The sending domain has a very low reputation at Gmail, and the message was blocked. Check with Blacklist check.

• 421 4.7.0This message is suspicious due to the nature of the content or the links within. To best protect our users from spam, the message has been blocked.

  The message was blocked because of its content or the links in it.