3CX Voicemail Troubleshooting Help

I’m running a 3CX Professional installation where voicemails have suddenly stopped being stored on the server and are no longer reaching users’ mailboxes. The PBX hasn’t been updated recently, so this isn’t tied to a new build or hot-fix... (Budget: $15 - $25 AUD, Jobs: Asterisk PBX, Linux, SMTP, System Admin, System Administration, Technical Support, Troubleshooting, VoIP)