Over the weekend I had several customers report issues with their email accounts.
When logged into Horde it would display a screen full of Invalid Address emails and Outlook would give an error like:
Receiving' reported error (0x800CCC90) : 'Your incoming (POP3) e-mail server has reported an internal error. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: -ERR Message 4 expunged.'
I traced this down to individual emails causing the issue, and when deleted, it would resolve the issue.
I now have discovered that in Imunify360 2.4-20 you changed the quarantine behaviour and have forcibly enabled in-place quarantines.
Imunify360 is now scanning email folders and will chmod 000 emails containing malware. This is causing the issue above to occur and breaks the email account for the user.
I have added /home/*/mail to my malware scanner exclude list and have reverted all of the emails it had quarantined to repair the broken accounts.
Hopefully you can fix this bug in an upcoming release!