Not responding means your computer has something going on which is interrupting Thunderbird. Computer could be performing updates on Windows or other programs like Adobe or any Games etc. Suggest you do not allow things to auto update, get them to auto check for updates, but ask you when to do it. Then you can get updates done and out of the way before running programs like Thunderbird. Suggest you do not allow any Anti-Virus product to scan Thunderbird files and folders on startup. Make Thunderbird files and folder exempt. Also do not allow Anti-virus to scan incoming emails, this is usually an option you can switch off within the AV product. It will still scan any attachment you open. It can cause more problems than it resolves. http://kb.mozillazine.org/Email_scanning_-_pros_and_cons If you have not make a backup of your Thunderbird profile then suggest you do it now. This is where it is located: * C:\Users\<Windows user name>\AppData\Roaming\'''Thunderbird'''\Profiles\<Profile name>\ * Make sure Thunderbird is not running; you must exit Thunderbird first. * Copy the 'Thunderbird' folder and paste it on eg: an external hard drive, then you will have a copy of everything. After making a backup.... It is much better to have smaller more organised folders for storage than a couple of large folders. Remember, emails are not actually stored in folders, they are written to a text file, one after the other in the order downloaded. So really you may have a lot of emails in one simple document. * Suggest you access your current organising of emails and move emails to better organisation. Anything older should be Archived. * See info on Archiving: https://support.mozilla.org/en-US/kb/archived-messages Once emails are backed up and sorted for storage..... How frequently do you compact folders? You should be doing it on a regular basis to remove all traces of old deleted emails. Inbox, Drafts, Junk tend to get the most deletions and so need compacting more often. I do it at the end of each day, but I suppose it depends upon how many emails you delete. * Clean up files by compacting each in turn. * Right click on folder and select 'Compact'. * Work through folders., one at a time. Performance: http://kb.mozillazine.org/Performance_%28Thunderbird%29

I would also advise you see if your computer needs to perform a defragmentation. https://support.microsoft.com/en-gb/help/17126/windows-7-improve-performance-defragmenting-hard-disk