If this is an IMAP account, this could happen if your Drafts folder is defined on the remote IMAP server. Open Tools/Account Settings/accountname/Copies & Folders, and under Drafts & Templates, make sure 'Keep message drafts in:' is set to Drafts Folder on: Local Folders. See if that eliminates 'not responding' errors.

Thanks for that advice. I've changed it over. I'll give you a shout if it still locks up, otherwise I'll mark it a solved. Thanks! :)

This hasn't actually fixed it. It doesn't seem to be doing it as much (although it could just be that I've not been sending as many emails...), but it is still doing it a reasonable amount. It also does a similar thing when sending emails, but not always - in fact, not normally. Any other thoughts? Sam

Do you have an anti-virus program scanning mail folders? If so, disable it. Also, right-click the Drafts folder, Compact; this will truly 'empty' the folder, even though it appears empty, i.e. old drafts have been removed from view, but still present in the TB profile folder.

I've tried that for a few days, but it's still doing it... (I've tried compacting and disabling that part of the antivirus.) It's starting to get quite annoying! Any further ideas? =P

(Also, I clicked on this question today to post this response, and it said "thank you for choosing a solution - I didn't do this (at least not intentionally - apologies if you thought this was fixed because of that!)

Try rebuilding the Drafts folder: select Help/Troubleshooting Information, click Show Folder to open the profile in Explorer, exit TB, go to Mail/Local Folders, delete Drafts (no extension) and Drafts.msf.

Restart TB and see if having a fresh Drafts folder makes any difference.

http://kb.mozillazine.org/Compacting_folders#Real_fix

Hmm... I've tried that for a while, but it still happens!

Should I just pack up my filters, then reinstall Thunderbird? (Nothing else that I need to back up, is there...?)

Thanks, Sam

Maybe it would help us if you show the help/ Trouble shooting information. Use the "copy to clipboard - button" and paste in here.

Ah, I didn't know about that. Just got it now.

 Application Basics

   Name: Thunderbird
   Version: 31.4.0
   User Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0
   Profile Folder: Show Folder

             (Local drive)
   Application Build ID: 20150109111741
   Enabled Plugins: about:plugins
   Build Configuration: about:buildconfig
   Memory Use: about:memory

 Mail and News Accounts
   account1:
     INCOMING: account1, , (imap) imap.googlemail.com:993, SSL, passwordCleartext
     OUTGOING: smtp.googlemail.com:465, SSL, passwordCleartext, true

   account2:
     INCOMING: account2, , (none) Local Folders, plain, passwordCleartext

   account6:
     INCOMING: account6, , (imap) imap.hermes.cam.ac.uk:143, alwaysSTARTTLS, passwordCleartext
     OUTGOING: smtp.hermes.cam.ac.uk:587, alwaysSTARTTLS, passwordCleartext, true

 Crash Reports

 Extensions
   Thunderbird Message Filter Import/Export Enhanced, 1.0.3, true, [email protected]

 Important Modified Preferences

   Name: Value

     browser.cache.disk.capacity: 358400
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 Graphics

     Adapter Description: Intel(R) HD Graphics 4600
     Vendor ID: 0x8086
     Device ID: 0x0416
     Adapter RAM: Unknown
     Adapter Drivers: igdumdim64 igd10iumd64 igd10iumd64 igdumdim32 igd10iumd32 igd10iumd32
     Driver Version: 10.18.10.3308
     Driver Date: 9-16-2013
     Adapter Description (GPU #2): NVIDIA GeForce GT 750M
     Vendor ID (GPU #2): 0x10de
     Device ID (GPU #2): 0x0fe4
     Adapter RAM (GPU #2): 2048
     Adapter Drivers (GPU #2): nvd3dumx,nvwgf2umx,nvwgf2umx nvd3dum,nvwgf2um,nvwgf2um
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     Version in use

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     4.10.6
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     NSS
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     NSS Util
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     NSS S/MIME
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Thanks! :)

One thing that has slowed down things is old nvidia drivers. I know thats not your problem, but update it anyway if you can. It helped me.

You can change settings in option/composition about if and when you save drafts

Oh yeah, they are old. It's a laptop that I bought as a full thing, so I didn't set stuff up on it. I'll update the drivers shortly.

I like having frequent autosave in case it crashes... but I guess if it means I have t wait 20 seconds every time it autosaves, better less frequent!

Thanks for the advice, but I still can't work out why it's happening! I'll try a reinstall when I get the time then let you guys know. :)

Just to be clear, did you set the Drafts folder on Local Folders for both accounts? For the cam.uc account, if you look under Tools/Account Settings/camaccount/Server Settings/Advanced, what is in the box for "IMAP Server directory" (should be blank), and is "Show only subscribed folders" unchecked?

http://www.ucs.cam.ac.uk/email/muasettings/thunderbird.html

I double checked, and it is correct, as you mentioned above.

It took me a while to actually get it to work, and this was one of the things I made sure was correct!

I'll post on here when I've reinstalled. In the meantime, I'm dropping the autosave time down (or up... dependent on how you look at it!). :)

So, just an update. I've extended the time between saves for drafts, so it basically just isn't saving drafts automatically. As such, it doesn't seize up. Occasionally it does when click send, but not often.

Thanks everyone for their help. :)