UBB.threads PHP Forum Software Community Forums UBB.threads Version 7/8 Support Forgot password mails not being sent

I just noticed that the "forgot password" function on my board is not working. It says "Password mailed" on form completion but no e-mail is received.

* Other board e-mail notifications are working fine
* php.ini has SMTP server set to localhost and port 25
* "Board e-mail address" is set correctly
* No errors related to this in the Apache logfile
* I was running ubb.threads 7.4.x before, but upgraded to 7.5.2 with the same problem

Where else should I be looking to debug this problem?

Update: After twiddling with random settings, the problem seems to be fixed. Not sure what was going on...