I'm able to save drafts to Drafts on Local Folders without errors. Do you need drafts saved on the IMAP server? Since gmail automatically saves sent messages, 'Place a copy in' should be unchecked in Copies & Folders, and the Sent Mail folder is the one to subscribe.

I'd like the drafts saved on the IMAP server and I'm getting an error message each time it saves. I'd prefer not to save it onto Drafts on Local Folders. Also I get an error message saying the message isn't saved in the Send box.

I unchecked Copies and Folders, but it still didn't work! :/

I just saved a draft to the gmail IMAP Drafts folder with no errors. Did you run the profile from TB 78 in TB 91, or create a new profile with 91? Are there any other apps such as antivirus that scan the TB profile folder?

Mmmm...well that's good news! I have no idea what running a profile from TB 78 or TB 91 means...could you walk me through it step by step to see where/what I need to check and what I would need to change?

Oh so sorry! I think I understand your question...I am running a profile I created in Thunderbird 78!

I don't know if reusing the 78 profile in 91 causes the drafts error, but I always recommend creating a new profile for beta versions or major releases, especially when a new version is just released. You could create a new profile from Help/More Troubleshooting, about:profiles, add a gmail account, and see if drafts save to Drafts on Gmail. Either the current default or new profile can be launched from about:profiles.

I created a new profile but I'm still getting the same error when I try to save a draft or when I send a message.

Oddly enough I don't have that problem with my non-Gmail account. It's with my Gmail accounts that I'm having this issue of saving.

Back to the previous question: what else is scanning the TB profile? What is the antivirus?

Nothing I believe is scanning the TB profile.

In order for us to better investigate this issue, we'll need some more information.

Could you please do the following?

1. Open the menu > Help > Troubleshooting Information, then click Copy text to Clipboard.
2. Go to https://pastebin.com, paste the info from your Troubleshooting Information page, use the Create New Paste button to create a page containing your info, then copy the resulting URL (address) of the page created.
3. Open a reply to this post, and paste the link to your troubleshooting information you just copied.

Next, we'll need you to provide answers to the following questions:

• Does Thunderbird work in Safe Mode?
• Do you use anti-virus and firewall software? What is the version?

Of course! Thank you for your help!

Here's the link you requested: https://pastebin.com/y9RhXWwi

I don't have any antivirus software that I know of.

I couldn't find Safe Mode but I could find Troubleshoot Mode. I tried that on. Thunderbird works, but I tried to save a draft, but I got the same error message.

using openpgp?

After a long struggle for several months, I eventually solved this problem.

In my case, the problem stemmed from the email shield of Avast, which switched the genuine certificate of imap.gmail.com:993 to Avast's silently.

By disabling the "Scan secure connections" option in the Email Shield settings of Avast, the original certificate was got back, and everything became normal with Thunderbird. Interestingly, only Thunderbird among email clients is sensitive to this issue.