TB 60.5.3 very sluggish email display with attachments

[yet another name]

since about a week displaying emails with large (e.g. 20mb) attachments is VERY sluggish, hangs for some time. Green progress bar displays, ... attachments are xml-files.
seems like xml-files are entirely loaded into content and everything hangs until finished (which takes WAY too long > 20-30s on FAST laptop with SSDs).
weird thing is, that in content a screenshot of TB is displayed (sometimes more than once) at random location(s) in mail content.
The emails have previously been downloaded to pc (POP3)

so 2 things seem to be happening:
- attachments are FIRST fully loaded before displaying content
- screenshot (of TB) is also being displayed in content

Win10 Ult., TB 60.5.3, P3740, 24GB RAM, 2x512SSD

[tanstaafl]

Moved from Thunderbird Bugs to Thunderbrid Support since you are not discussing workarounds for a confirmed bug filed in Bugzilla.

[tanstaafl]

MIME parts of demand is a feature that makes loading a message from a remote folder in a IMAP account smarter/faster by doing things like not fetching an attachment unless its explicitly opened. But you're using a POP account.

My first thought is that the mail folder is corrupt. That happens mainly with the inbox folder, due to a combination of lots of messages and lots of deleted messages (they're hidden but not physically removed yet as compacting hasn't occurred yet). Does this problem only occur with the inbox folder? http://kb.mozillazine.org/Compacting_folders

Did this problem occur out of the blue or shortly after a upgrade? It wouldn't hurt to see if it occurs in safe mode (help -> restart with add-ons disabled) to rule out it being due to an add-on.

Thunderbird uses mbox files by default for storage. Each mbox file stores all of the messages for a folder, and is named after that folder. Its not a database, its one message stored after the other in a plain text file. Thunderbird has support for another storage format called maildir. That stores each message in a separate file (as a .eml file but without the file extension) . There is no need to compact a folder (in fact you can't) with maildir. One possible solution would be to switch storage formats for your account to maildir but I suggest you don't consider that until your situation is clearer.

[tanstaafl]

http://kb.mozillazine.org/Performance_-_Thunderbird might give you some other ideas, though its meant for problems that are not message specific.

Any reason you haven't upgraded to 60.6.1? I have no idea if your problem is version specific but its easier to help somebody who is using the latest software.

[yet another name]

gone in 60.6.1 but:
when deleting a mail it still "hangs" on emails with an attachment (1MB or more). It takes a few seconds for list from which I'm deleting a mail to rebuild.
At first pretty scary because when deleting a mail entire mail list and mail content goes blank and nothing happens for a while...