What does "Mail Deferred:" mean in Linux Logwatch

I am just analyzing my logwatch logs, and I see the following entries:

 SMTP SESSION, MESSAGE, OR RECIPIENT ERRORS
 ------------------------------------------

 Mail Rejected:
       Total:  6

 Mail Deferred:
       Total:  229

 Total SMTP Session, Message, and Recipient Errors handled by Sendmail:  235

 ---------------------- sendmail End -------------------------

I only use sendmail for logwatch, so what is causing all these errors, and especially, what are deferred emails.

Solution 1:

Deferred mail is simply mail that was unable to deliver to the sender and has been added to the mail queue ( you can view it by mailq or postqueue -p).

You can try to resend (flush) all those messages with sendmail -q, which will attempt to send again.

One reason it could be doing this is if your server's DNS listings (/etc/resolv.conf) are not functioning, you will not be able to deliver mail outside the local domain. And yes, I've made the mistake before in the past. It might be what's happening on your side, but then again, maybe not. Just trying to give tips. :)

Either than that, there's no easy way to see what is causing it. I'd recommend to check /var/log/mail.log, /var/log/mail.info, /var/log/mail.err, and /var/log/mail.warn for any clues to see why the messages might not be delivering. It would most likely be in mail.err if something wrong is happening while sending.