One rogue VM (secondary) account in a cluster of other VM accounts refuses to work.

I have one VM account (one of several secondary accounts) which has refused to accept input for some weeks. Thunderbird is email client.  Up to 28th May VM/ThunderBird had worked without issue across a score of accounts on Ubuntu 22.04 desktop.

There are no signs of email bouncing. They are swallowed now by this black hole account.

I have tried changing rogue account password to no avail. Utter confusion in navigating VM links and ThunderBird dashboard probably screwed up other accounts.

I also have ThunderBird on Windows (dual boot which I rarely use). I cannot get into VM server through ThunderBird Windows which I just tried. I am back in Ubuntu as I pen my journey through VM and ThunderBird.

I can forward locally from one VM account to others. But just NOT to this particular rogue account.

What I would like to do is apply a single password to every account (seen from Ubuntu and later Windows). Once all accounts (a score of accounts) are working I can if necessary apply unique password per account. But I will need to write an automation script (later) for this workflow.

There is further complication since I am asked now to use a non VM email account for verification. So Gmail accounts (seen in ThunderBird alongside VM) are used.

I read a tip in this forum to test email accounts using curl. I have started writing a multi account curl script for this quick analysis on a batch of accounts but right now I just need this rogue account to come back into service.

Any VM/ThunderBird forensic users here to offer advice?

Any VM “MRI scan” available? How are multiple passwords synced between VM and Thunderbird? I would like a one stop shop for multi account administration.

Further Thoughts.

Added note:

This particular secondary VM account had worked for some time. Then I used it as an MX forwarding address from a domain in construction. Google Domains transferred their global estate of domains to SquareSpace and whether concidental or not my problems occurred then. I have since deleted domain MX records forwarding rule for that domain which pointed to this non receiving secondary account. And I am looking back through the correspondents I can view in archived profile so that I can systematically isolate this secondary account and perhaps delete it after I have extracted profile for backup and perhaps import to another account. There are multiple actors in play. SquareSpace, VirginMedia, ThunderBird.