Comment 8 for bug 2060534

Thanks for the detailed answer.

> Sounds like the Sent-1 file is so big it's not possible to do compacting maybe because either Thunderbird is interrupted during the compacting eg: shutdown, crash or receiving mail into the folder being compacted, maybe another program is scanning the file or it's possible that you might not be able to compact a large folder because you don't have enough free disk space or memory or there is some type of corruption in the file. 50GB is very large for a single text file and it looks like it's been failing to compact for a while, so is full of old deleted mail.

I have 1 TB of free storage so it's not out of disk space (except when Thunderbird fills it all up with nstmp).
Normally, I never delete things from sent items (I have messages as old as 2005 there).
I already deleted the Sent-1 file, thinking Thunderbird will rebuild it from the server but it looks like it's satisfied with Sent-1.msf and did not recreate Sent-1.
I did not run into the problem since I opened the bug report.

> Does it say anything in the Error console?

Manually compacting `Sent` works now and there is nothing printed to the Error Console.

> Is this checkbox selected 'Compact all folders when it will save over' ?
Yes.

> What is the number of MB set ?
20 MB

> Is this checkbox selected 'Ask every time before compacting'?
No.