I'm having an issue with a customer and I'd like some advice on how to look for the problem.
A customer contacted me and said that she can't see email in her box that she knows was sent to her. I logged into her mail and I didn't see the mail either. (It was sent about 10 minutes prior).
I logged into the server (cPanel running Dovecot, Roundcube's most current version on cPanel, 0.3-stable.cp3) and looked at her physical mail box and the message was sitting in her /cur directory and had a time stamp of 10 minutes prior.
I tried refreshing, hitting the "check for new mail" button and it wouldn't show up in Roundcube.
I hit the settings icon to check her "check for new message timer", which was fine, so no change, and when I hit the email icon, the message appeared in both of our displays. (a bit of a refresh delay on her side).
It is clear that the message was delayed at least 10 minutes before I started looking at the problem and at least another 5 minutes after I verified it was physically available myself. Once the problem clear, any message sent showed up as expected after that.
What could be causing this problem? Where do I start looking?