Hi,

Hello.

My Thunderbird instances suddenly started to choke on sending emails to smpt.office365.com (not sure for others).

I had similar issues but with mailbox's SMTP servers.

Both my 139.0.2-1 and 143.0.1-2 instances have the same problem:

I started having problems with Thunderbird around the same time with Firefox after updating both. Firstly, I thought my VPN was causing issues, but I later confirmed that wasn't true. Not sure if Mozilla did an oopsie or if it was just a coincidence, with something else entirely, breaking Firefox/Thunderbird or its configuration.

1. I click 'send' and TH is stuck on "Sending message" dialog box. 2. devtools shows error in console:

08:57:41.360 NS_ERROR_FILE_NOT_FOUND: Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIFile.fileSize] SmtpServer.sys.mjs:598

3. When I click 'Cancel' in dialog box from (1) then, 'Send' again the problem repeats.> 4. When I wait for TH to give up and click 'Send' again message is sent successfully.

Anyone sees similar behavior?

Almost everything described above is how it happened to me. Now, I don't have a nice solution and don't believe I ever got to the root of the problem... but I needed it fixed fast (and I had already fiddled with it for an hour or two), so I decided just to reinstall both Firefox and Thunderbird and delete their configs and cache (while retaining their database files so I wouldn't need to re-import all of my contacts and calendars the hard way). If somebody else doesn't come up with anything better, I'm just leaving this here to let you know that the nuclear option resolved my problems (and could, very well, be the only worthwhile option, but I honestly doubt that). Sincerely, Gabrijel Jakovljević PS: I remember seeing somebody else have issues (the same stuttering) in Firefox, on the RC, and I don't think it coincidental that both he and I had broken browsers after an update and that the same update came really close to the TB update, which ended up breaking my instance. Could be wrong, though. PPS: Also, are you using vanilla TB, or do you have a fork / custom user.js?