Upgrade Thunderbird?

I'm having a new problem sending some emails with pdf attachments in Thunderbird. I get a message saying there's an esmtp protocol deviation and the email doesn't go.

I see that I have Thunderbird v 78, but that there's a v 91 available from Thunderbird itself.

Maybe the new version would solve my problem.

Should I upgrade to v 91 now in hopes that it will solve my problem, rather than wait for Ubuntu to do it?

You could install the newer Thunderbird as a snap. Version 91.1.1 is in the latest/candidate channel. Such installation can co-exist with your current version.

It can be doubted whether the problem sending a PDF attachment is due to Thunderbird, and to that specific version, however. It is not expected that upgrading will solve that issue.