esmtp protocol deviation

[lesliek]

I'm using Thunderbird 78.13.0 (64-bit) with Ubuntu 20.04.3 LTS.
I have a problem that's just arisen recently.
Lately, when I try to send an email with an attachment, I'm told that there's been an esmtp protocol deviation and the email, although it appears in my Sent file, doesn't actually go.
I turned on logging and the only additional information I could see was that the code generated as a result of the error was 421.
When, instead of using Thunderbird, I use my ISP's webmail, I can send the same email and attachment without any problem.
Is there some way I can overcome this problem?
Thank you,
Leslie

[tanstaafl]

There was a recent bug fix that I think fixed this. It was due to Thunderbird requesting some capability that it didn't need, that some smtp mail servers didn't support. The fix was to stop asking for that capability. I can't spot any mention of the fix in the 78.14.0 or 91.* release notes so its possible it was fixed in a "daily" release (not ready for general release yet).

Sorry I can't remember more. If I find where I came across the information I'll let you know.

If you have more than one account try using the other accounts smtp server as a workaround.

[lesliek]

Thanks for your reply tanstaafl. If you find any more information, I'd be grateful to receive it.

For now, whenever I get the error message, I'll switch to the ISP's webmail and send the attachment that way, since that seems to work.

Thanks again.