I use ISP Config 2.2.17 and RoundCube and have noticed that when a mailbox goes over its quota, I am unable to delete messages from it with RoundCube. The problem may be present using Outlook or another e-mail client, but I haven't tried. I get around this by either forcefully deleting all e-mails in a user's Maildir from the command line, or increasing the quota then allowing them to delete the messages. Has anyone heard of this problem before or got any suggestions?
Some time ago I've heard about a problem with deleting e-mail with Round-Cube. It was a bug in this application.I don't know if it's been removed or not. Maybe You should try another webmail client like Squirrellmail and try to do the same.
Thank you for your quick response. I can delete e-mails just fine, just not when I am over quota. When I try, it appears to delete the message, though a refresh has the message come back.