This article applies to:

• Trustwave MailMarshal (SEG)

Symptoms:

• An outbound message is not delivered to a remote recipient
• The local sender may receive a non-delivery report
• The MailMarshal Sender log shows an error response similar to the following:
  RX: <550 5.7.1 Unable to relay for a@b.c>

Causes:

• This error is not generated by MailMarshal and in almost every case the issue is not a MailMarshal issue.
• The mail server that MailMarshal tries to send the message to is rejecting the mesage.
• DNS Mail Exchanger or A records that are published for the recipient domain point to a server that does not accept mail for the domain.

Resolution:

1. Verify that MailMarshal does not have a custom routing configured for the recipient domain.
2. Contact the recipient organization to report the issue and find the acceptable domains.