I got to fix the problem with a similar process as kamome described, but (a) the process was a pain in the posterior because massive amounts of deleted mails reappeared in their original folders which then had to be hand-deleted, and (b) the problem reappeared just a day or two later.
At that point, I gave up and returned to Thunderbird.
I got to fix the problem with a similar process as kamome described, but (a) the process was a pain in the posterior because massive amounts of deleted mails reappeared in their original folders which then had to be hand-deleted, and (b) the problem reappeared just a day or two later.
At that point, I gave up and returned to Thunderbird.