Thunderbird Offline Limits
I’m a long time user of Thunderbird and recommend it over most email programs for email usage. I’ve found problems with the way Thunderbird handles offline email. I have a client that has 50,000 emails in his Archive folder. The offline behavior of Thunderbird for this client is very flaky.
A little background. There are different ways to store emails in files. One way called mbox stores all emails of a folder in one file.