Since Gmail uses 2-Step verification (or appears to be silently introducing a need to enable it for some users), did you try the solutions described here and here?

The issue(s) could also be caused by a recent Thunderbird update - version 45.4.0 was released Oct 3 - and any firewall or internet security related software on your system. You could try to remove Thunderbird from allowed apps in the software and re-add it again, either directly or when asked by the software as soon as Thunderbird connects to the outside world.

Two separate PCs, one Win 10, one Win 7 pro same problem. Both have v 45.4. No two step authentication, no gmail password changes, no changes in Bitdefender or Malwarebytes. Firewall on both PCs is OFF. Added gmail account to the dreaded Outllok and it works great. THe inbox works fine and email comes in. If I click on any other folder, like to look in the spam folder, there is a long delay - sometimes timeouts. Any ourgoing message takes very long and sometimes times out and has to be resent. Thanks for any help. I use the 2 gmail accounts a lot and I don't want to move away from Thunderbird after so many years of using it.

OK, 2 separate PCs. Could the issue have started after upgrading TB to version 45.4? Of course you could try reinstalling the/a previous version on one of the machines to quickly rule some things out. You could view the TB update log in Options > Advanced panel > Update tab > Show Update History to get some indication of whether the issue started around the time of an update as well as the previous version used, and browse to that earlier version using the link if needed.

I mentioned the 2-Step Verification, but was mainly aiming at the requirement to turn on less secure apps if you are not using it. Did you try that? See this question for more info.

On the other PC, I had a copy of Thunderbird 36.x becasue I could not figure out how to get a newer version downloaded. I installed that and it picked up all accounts ok and gmail worked fine. If I am at 45.4 , what version should I roll back to to get around this problem. Less secure apps was turned on.

OK, here’s a few things you can do:

- First, please make sure you have read and followed all steps described here, then check whether the issue is resolved.

Additionally/afterwards when not:

Option 1

Since you are running Bitdefender (which is known to be a possible culprit with TB), - Try disabling it first, restart your system and see what happens, or - Disable SSL scanning (may be called Scan SSL) under Web protection in the Bitdefender product, which should reside either under Modules or Protection. See what happens then, re-enable it and try again.

If things work as epected when Bitdefender is disabled, it should "learn" about (or keep up with) the changed version, as written above.

Option 2 (sort of lucky guess, but related)

- On the system using 45.4, open the Thunderbird Profile folder using Help > Troubleshooting Information > Open Folder (the button next to Profile Folder.) More info on Profiles can be found here. - Close Thunderbird. - Delete the files key3.db and cert8.db from the profile folder, or move them elsewhere. - Start Thunderbird and see if things work as they should.

The point here is to remove certificate stores that may be in the way or be damaged, though it would be a coincidence this would only affect 45.4, which I cannot explain (yet) in case it would help. The files should be regenerated automatically.

Option 3

- Remove the account (or one of them) on the system running 45.4. Since you are using IMAP, this could do no harm, but you could consider creating a backup of you profile folder first. Safest is to copy the entire folder to some other place - see the link above for where to find it, and copy the folder when TB is closed. - Re-add the Gmail account using Account Settings > Add Mail Account (bottom left). - Additionally and when done, check whether the (new) server and authentication settings match the ones described in the Help link above, as well as with the ones used on the other PC. Are they similar?

Option 4

You could try reinstalling older versions sequentially in order to find the "regression range". I’m a little puzzled since you wrote you installed version 36.x on the other system that works fine, but that version was never released, though you might refer to 38.x. If you take a look at the update log entries first as suggested above (on one or even both systems), you can find out what version was installed when things were still working, let’s say 2 weeks ago - after all I can’t tell if the last update happened e.g. a year ago or always applied automatically and hence the previous release was used, which was 45.3. (See here for a list of TB Release Notes, although the v38 releases are not listed there.) Keep in mind that any unnoticed program update by the firewall (Bitdefender) is important and may cause a particular version to work as described above, so if any version works, that could still be the cause so eliminate that first under Option 1.

Here are the links to some previous versions for your system: 45.3, 45.2, 45.1.1, 45.1.0, 45.0, 38.8.0, 38.7.0. If needed, I’d start with 45.0.

You have really been a big help to me. On the alternate PC, I had loaded 36.x . I will go back and load 45.0. If that seems ok, I'll load 45 on my mail PC.

Although this was a big help in troubleshooting it did not solve the problem on 2 different PCs and versions. Still timeout when moving between folders or sending an email. One PC: Tried v 45.0 same problem Tried back to 38,7 same problem. Tried v 45.4 on a pc with no antinvirus. same problem. Have two different ISPs here. Same for both Time Warner and ATT. Lengthened the timeout to 120. Added each gmail account to Mailbird - no problems. Same with Outlook software.

Can you check Thunderbird’s Connection settings (Tools > Advanced panel > Network & Disk Space tab > Settings) and make sure "No proxy" is selected?

No Proxy. That is one of the first things I checked. Firefox is also set on no proxy. Email to the inbox comes in fine. I have one other sub folder under INBOX. If a message lands in there, when I click on ihat folder I get a timeout, so bad that I cannot read the message and have to log into my gmail through firefox. If I try to send a message I get a timeout. This particular account is still v 45.4 . If I click on any folder other than INBOX, I get a timeout. I have used Thunderbird 9 years and I don't want to abandone it. I have 26 email accounts in my Thunderbird and Gmail is the only one with a problem. Previous to this issue there long delays in Thunderbird accessing gmail folders and it gradually got worse so that now it is alnost unusable for Gmail accounts.

A few other suggestions:

- Unsubscribe from the "All Mail" folder, exit, and then delete both "All Mail" and "All Mail.msf files. The All Mail folder may double the amount of disk space used by Thunderbird (see here and here).

- Go to Tools -> Account Settings -> <Gmail account> -> Copies & Folders and uncheck Place a copy in…. Gmail's SMTP server automatically saves a copy of any message you send in the Sent Items folder, so this is to avoid Thunderbird doing things twice, save disk space and decrease timeouts. (see here).

- Open Tools > Options > Advanced > Config Editor (about:config), accept the warning and look for mail.server.default.use_condstore. Make sure it is set to false (default), and double-click it if not. See bug 693204 for more info; it should be disabled by now by bug 912216, but chances are it is not.

The links may offer more info. Could you report back?