Every so often RT 3.6.6 just stops sending email. If you display a ticket, you normally see a line about an email being sent after each comment or correspondence. When in RT fail mode, those lines just aren’t there. Restarting apache cures the problem. I went into the apache error.log (interestingly the one for apache, not the one for the RT virtual host) and found this:
[Thu Aug 21 01:40:53 2008] [crit]: Could not send mail: Couldn't run /usr/sbin/sendmail: Cannot allocate memory at /usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm line 334.

Stack:
[/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:334]
[/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:288]
[/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:107]
[/usr/share/request-tracker3.6/lib/RT/ScripAction_Overlay.pm:242]
[/usr/share/request-tracker3.6/lib/RT/Scrip_Overlay.pm:507]
[/usr/share/request-tracker3.6/lib/RT/Scrips_Overlay.pm:195]
[/usr/share/request-tracker3.6/lib/RT/Transaction_Overlay.pm:181]
[/usr/share/request-tracker3.6/lib/RT/Record.pm:1466]
[/usr/share/request-tracker3.6/lib/RT/Ticket_Overlay.pm:746]
[/usr/share/request-tracker3.6/lib/RT/Interface/Web.pm:467]
[/usr/share/request-tracker3.6/html/Ticket/Display.html:107]
[/usr/share/request-tracker3.6/html/Ticket/Create.html:375]
[/usr/share/request-tracker3.6/html/autohandler:291] (/usr/share/request-tracker3.6/lib/RT/Action/SendEmail.pm:349)


Googling for portions of that error message lead me to this thread.

My munin graphs show a lot of swapping for that host. So I’m gonna crank up the memory and look again some other day.