We’ve been using RT 5 for some time without issues. Today I noticed that one user had replied to a ticket and the ticket got updated but it didn’t trigger a notification email for us (therefore the ticket was sitting there as we supposed there was no update).
I then replied to the user and RT refused to send out the mail message again. I noticed that in the ticket thread the failures were marked as:
“The RT System itself - Sending the previous mail has failed. Please contact your admin, they can find more details in the logs.”
This is what I found in the logs:
Sep 17 10:08:27 helpdesk RT:  firstname.lastname@example.org: Could not send mail with command
/usr/sbin/sendmail -oi -t: open2: fork failed: Cannot allocate memory at /home/rtuser/rt5/sbin/…/lib/RT/Interface/Email.pm line 937.