451 Local error in processing

Gmail

• 451 4.3.0Email server has temporarily rejected this message.

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

• 451 4.3.0Multiple destination domains per transaction is unsupported. Please try again.

  The sending server put recipients from several domains in one transaction, which Gmail does not accept; it needs one transaction per domain.

• 451 4.4.2Timeout - closing connection.

  The connection stayed idle too long and Gmail closed it. The sending server retries; if it repeats, check the network and the sending server.

• 451 4.5.0SMTP protocol violation.

  The sending server did not follow the SMTP protocol (RFC 5321): the problem is in its software or configuration.

• 451 4.7.23ip-address The sending IP address for this message doesn't have a PTR record, or the PTR record's forward DNS entry doesn't match the sending IP address. To protect users from spam, your email 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.

• 451 4.7.24The SPF record of the sending domain has one or more suspicious entries. To protect our users from spam, email sent from your IP address has been temporarily rate limited.

  Gmail finds one or more entries of the sending domain's SPF suspicious, so it limits or blocks the mail. Review every mechanism in the SPF record. Check with SPF generator.

• 451 4.7.26Unauthenticated email from domain-name is not accepted due to domain's DMARC policy, but temporary DNS failures prevent authentication. Please contact the administrator of domain-name domain if this was a legitimate email.

  The From domain has a DMARC policy that rejects unauthenticated mail, but temporary DNS failures prevented the check. Make sure the domain's DNS servers answer. Check with Email DNS check.