Howard Miller

BigBlueButton is built in to core Moodle, now. You don't need the optional plugin.

This is both not a Moodle problem and hard. Even a proper MTA , Postfix can't do this "out of the box".

You could have a look at something like this - https://ngocquyetlinux.blogspot.com/2013/05/limit-mail-with-policyd.html

...and also configure Postfix to be a "smart host" to forward all your mail. This is all tricky stuff and, to be honest, I'd try to find some other solution.

It's hard to believe that cron is directly related to this. Although, it could easily be going wrong *as well*.

Moodle is a big application and eats ram. You're definitely going to have problems with insufficient memory.

enable allowaccountssameemail ??

The setting is to be found at Site administration > Plugins > Manage authentication

BUT... having accounts with duplicate emails may not be a good idea. If you don't have a specific reason for needing this then you might be better considering why you are trying to create new accounts that use emails that already exist.

The obvious (and so probably wrong) solution would be that you had created it with "Valid until" set to something.

How are you creating the tokens? Also check that you are not deleting anything related that might be taking the token with it.