When OMR returns a "Mail delivery failed" message, In the bounce email from OMR, the notice will contain the "exact" reason the recipient mailserver's refused your message. This is the part just after SMTP error from remote mail server after [...].

Failures occurring "after RCPT TO" or "after MAIL FROM" generally indicate the recipient mailserver has an issue with the To: or From: addresses. For example, that site could have an issue with the From: address if previous emails you sent there were being flagged by users as spam. If the error occurred "after end of DATA" this usually suggests that site's spam filters have a problem with your message content (some sites for example will not accept heavily formatted HTML email, or certain file attachment types).

Some sites do not reject what they consider to be spam; instead they "graylist" the message so that the sender (OMR in this case) continues to retry. In this case OMR will faithfully re-try delivery for up to 24 hours before canceling and sending you notice.

These error messages can help suggest what is wrong, however since the reason is provided by a third party TZO can not make any claim to their accuracy. In a small number of cases the error message is mis-matched, indicating some type of problem but not necessarily the one claimed (errors "after RCPT TO:" when the site policy really objected to your email's "MAIL FROM:" for example).

The best resource for working out what the error means and how to fix it is the recipient themselves. If their mailserver is blocking their receipt of email they should have the ability to whitelist your email, or to notify their email administrator to contact you for troubleshooting steps.

This FAQ last updated: 04/29/2010 - 16:44