I've been using the Thunderbird e-mail client for years on three different operating systems: XP, Vista, Windows 7.

On all of these operating systems, it has always had the problem of e.g. I'll be writing an e-mail and suddenly it will just freeze, I can't type, and 10 or 20 seconds later it will "come back" and I can type again. When I look at the task manager when it does this, the CPU spikes to 100% during these times and the guilty process is Thunderbird.

The problem is not always the same:

  • on XP it started out fine and these black outs got longer and more frequent
  • on my Vista installation it would happen only once every 20 mails
  • now on a new installation of Windows 7, it happens almost every e-mail I type and often when I pull the scrollbar down it will freeze, "(Not Resonding)" will come up in the title bar, and I have to wait 20 seconds before I can use it again.

What could be causing this? Has anyone else had this problem with Thunderbird?

  • 2
    What do you use Thunderbird for... POP or IMAP? News? Feed Reader? What anti-virus/malware software do you use? Any other software running that could be causing it? What kind of Firewall do you use? – Richard Oct 25 '09 at 14:25
  • I have a new windows 7 installation using the new microsoft antivirus software (free), I use thunderbird for POP emails, rss feeder (60 feeds), default windows firewall, I do e-mails that go back 2 years, perhaps it is indexing them or something will have to check, thanks. – Edward Tanguay Oct 25 '09 at 14:39
  • It happens to me, too. It's almost enough to make me drop T-bird. But Outlook is my only alternative, so I come to my senses and live with it.... – Joe Casadonte Oct 27 '09 at 14:01
  • This is happening to me on a Windows 7 64 bit machine but only when I first start TBird. Once it gets past the freeze, it will function normally until it is shut down. – JCL1178 Aug 18 '11 at 17:19

10 Answers 10


From mozillaZine Application not responding :


Thunderbird stops responding and may use large amounts of processing power.


In some cases, the problem can be caused by a mail summary file (*.msf) file being corrupted. This can occur when your folder is mildly corrupted due to not compacting it regularly. A quick and dirty fix is to:

  1. Exit Thunderbird.
  2. Find your profile folder.
  3. Open the folder containing your stored messages. For example, if you are using the Global Inbox, this would be the "Local Folders" folder inside the "Mail" folder. Otherwise, it's a folder named after the mail server, inside the "Mail" folder. For example, "pop.gmail.com" if you're using gmail.
  4. Select the *.msf files and delete them.
  5. Restart Thunderbird.
  6. Wait for Thunderbird to recreate the mail summary file(s).

If that doesn't work, it may be because your folder is too badly corrupted. See the second part of the "Compacting doesn't seem to work" section in Compacting folders.

If the problem occurs when sending a message, try re-configuring your anti-virus program so it does not check outgoing messages for viruses.

In some cases, the problem is caused when Thunderbird has trouble detecting and filtering junk (spam). This may be caused by a corrupted training.dat file. It may be necessary to delete this (Tools -> Options -> Privacy -> Junk -> Reset Training Data -> OK) and retrain the [Mail Controls].

  • I'm in the process of going through the second part in Compating Folders, and when it's busy rebuilding the index at least, Thunderbird hasn't yet frozen once, not even when I compose an email which has always triggered the freeze before. Hoping it stays fixed after it's done bringing my folders up to date. – Jeff Welling May 25 '11 at 3:02
  • No dice. It hadn't even finished what it was doing when the lockups returned. :( – Jeff Welling May 25 '11 at 18:22
  • @Jeff Welling: An addon can be responsible for it. If this isn't the case, you should ask the question on the TB forums. – harrymc May 26 '11 at 17:44
  • 1
    Removing the msf files really sped up my thunderbird in linux: find ~/.thunderbird/*.default -name '*.msf' -print0 | xargs --null rm – Joe Oct 19 '11 at 3:40

Perhaps it's some kind of add-on? Try writing a couple of emails without any on.

If that solves your problem, try turning them on one by one to see if you can recreate the issue.

  • good idea, but I have no add-ons excepte the Mozilla talk-back which is not enabled. – Edward Tanguay Oct 25 '09 at 12:56

Thunderbird is lovely but resource-consuming.
On my station it hangs exactly as described in your example when it receives new messages and the antivirus (currently AVG) scans them.
IMHO Thunderbird hangs while waiting the return of the message by antivirus.

  • 2
    So change your antivirus - don't blame Thunderbird. – harrymc Nov 18 '09 at 12:31
  • I have the similar freezing problem, but I'm on a Mac with no antivirus software. If it wasn't for the fact that I didn't have AV software, that's what my first guess would have been too. – Jeff Welling May 25 '11 at 1:56

I had the same issue. I found out that my signature image was causing the issue.It was located in my office server and when I am trying to send mail from home TB hangs. I changed image location to my laptop and everything is fine now! :)


I had problems with the Windows Search integration (in Windows 8.1). Once I turned that off, Thunderbird was speedy as a, well, bird.

To turn it off, Tools > Options > Advanced (General tab) > Remove tick from “Allow Windows Search to search your messages”


Maybe its a problem with automatic mailbox defragmentation? You can turn this feature on an off.

I'm using Thunderbird since its very beginning and had never such problems.


Try using Process Monitor from Sysinternals to see what it's doing when it hangs.

Process Monitor is an advanced monitoring tool for Windows that shows real-time file system, Registry and process/thread activity. It combines the features of two legacy Sysinternals utilities, Filemon and Regmon, and adds an extensive list of enhancements including rich and non-destructive filtering, comprehensive event properties such session IDs and user names, reliable process information, full thread stacks with integrated symbol support for each operation, simultaneous logging to a file, and much more. Its uniquely powerful features will make Process Monitor a core utility in your system troubleshooting and malware hunting toolkit.


I found that if I make thunderbird run in compatibility with Windows XP SP3, it starts working as normal again. Dunno why but been working for a day without any further problems. Hoping it keeps on working.

  • Forgot to mention this was on Thunderbird 17.05 on Win8 Pro 64bit and downloading from gmail – Terence May 9 '13 at 10:11
  • You can edit your own answers with more info. No need to comment on them. – Brad Patton May 9 '13 at 10:40

I had the same issues on my laptop but not on my desktop. I was running windows 8.1 on both machines. The only difference was my internet security. Laptop had Mcafee, Desktop had Nortons/Symantec. I changed over to Nortons and have had no more problems.


The following process helped me out in the above issue:

Problem statement: when launching TB, it hanged up for some 20 seconds and a pop-up window advised me that a scipt file is still running. It is irrelevant wether or not you let it run further, or stop it, the issue persists.

Solution that resolved the problem : - open up AVG user interface (or any other virus remover app) - go to settings , then choose Advanced Settings in the menu - select Exceptions --> Add exception - choose Folder from the options, and browse and select the folder where Thunderbird has been installed. - you may want to repeat the above line and also choose Applications and browse for the Thunderbird.exe file, as well.

--> Thunderbird starts in miliseconds from now on.

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