Turned out my ISP had switched to a completely different backend email solution since Nov 15, without notifying anyone. The consequence of which was outgoing mail was not longer relayed except for via dedicated accounts that made it non workable for messages from the forum.
Had to subscribe to a SMTP relay service provider to get outgoing working again. Messages from the Forum to mail is now working again.
Had to subscribe to a SMTP relay service provider to get outgoing working again. Messages from the Forum to mail is now working again.