Deleted emails are not removed until you compact. It is on the file menu (alt+F)

and the cache is rarely emptied, you should not be backing that up at all.

I do compact folders at least once a week. I just back up the whole profile directory and it doesn't seem right that the number of files increases by about 20% per week. I only get about 30 - 40 emails a week and delete most of them. I'm concerned about running out of room on the thumb drives I use for backup. This behavior only started in the last 3 months or so.

Compacting folders is unrelated to the cache. The cache in Thunderbird essentially does the same as in Firefox - caching stuff loaded from the Internet. An increasing number of files isn't necessarily a concern, as long as the file size is small or even zero. Deleting the cache folder is useless, as the file and folder structure will be rebuilt automatically. By default the cache folder is not part of the profile, and hence wouldn't be backed up with the profile. The default cache location is C:\Users\<user-id>\AppData\Local\Thunderbird\Profiles\<profile_folder_name>. Why that isn't the case in your set up I don't know. In any case, you can control the cache location with this pref: browser.cache.disk.parent_directory <path>

This helps explain my problem. Two of us share the hotmail account (on a single PC) so TB is set up in the Public user account and each user has an ini file that points there. Public/AppData had no sub-directories except Thunderbird so I set up Local & Roaming directories, moved Thunderbird to the Roaming dir, moved the cache and cache2 dirs elsewhere and opened TB but it still created a new cache2 dir in the Roaming profile dir but no cache dir at all. Should the 'browser.cache.disk.parent_directory <path>' line go in the ini file, will it also relocate 'cache2', and could you be more more specific on the syntax? Also can I periodically delete cache and cache2 without ruining anything? Thanks, Scott

I have no idea what you mean with 'the ini file'.

You can set the pref in about:config (or Config Editor via Options - Advanced). If it doesn't exist yet, create it as type 'string'. The value is the absolute path to the desired directory. The 'cache2' directory will be created automatically underneath when Thunderbird is restarted.

Also can I periodically delete cache and cache2 without ruining anything?

The 'Cache' directory is obsolete. You can set the size of the cache via Options. I don't see the point to use a cache when you want to clear it periodically. Just leave it alone.

Thanks for your help. In the end it seemed easier to alter the backup software to exclude 'cache2' than mess with TB.

Now you have that, include global-message-db.sqlite. in that exclusion

A huge file that is not required. it will be regenerated if deleted. but not including it will save significant space and time. ALso check if Thunderbird is creating mozmsg folders and mozeml files. These are solely for windows search to index mail and really have little value in the backup either. On initial installation you are asked if you want windows search to index mail. Saying yes uses a lot of space for in my case nil return. I turned it off and manually deleted the 100,000 mozeml files in my profile.

Thanks Matt. I'll exclude it - fortunately I don't have the moz stuff.