A number of questions submitted to Ask Email Guy today were due to one of the issues below, so I've responded here rather than publish each individual comment.
For a few hours this morning, some users received a warning message when logging in to Web Mail that the site security certificate was expired. This was fixed within a few hours, and was due to a network change that inadvertently made the wrong security certificate active on a few of the servers. It was corrected this afternoon. During that same time period, Web Mail was unavailable to some users and displayed the "Down for Maintenance" page. Both issues were corrected this afternoon, and I apologize for the inconvenience.
On the previously-discussed issue of disappearing subject lines on Mozilla-based browsers (Netscape, Firefox, Mozilla), we are currently testing a fix and hope to deploy it to production in a few days. In the meantime, please try the suggestions here. This problem also appears to cause an HTTP Status 500 error to occur in Netscape browsers under certain circumstances. That should also be resolved with the fix.
Another problem in the recent 5.13 release that has been reported by some users is that if they delete a message while using the Preview window, then after the list refreshed some unread messages above that one would not show up until the user logged out and back in. We are also currently testing a fix for this, to be released at the same time as the issue above.
Lastly, some users report that when forwarding messages with attached files, the attachment isn't being sent to the recipients. This seems to occur only when the filename contains spaces, and it is also fixed and waiting to be deployed to production.
Hopefully in a few days these three new bugs that were introduced in the 5.13 release will be fixed for good. Thanks for your patience in the meantime.