Sharing profiles - mail
From MozillaZine Knowledge Base
If you copy a profile to a new directory within the profiles directory, Thunderbird will ignore it. Thunderbird looks in the profiles.ini file to find what profiles exist, and where they are. That file is in a fixed location on your boot disk, whose location partially depends upon what operating system account you logged in.
You can create a profile anywhere you want with the Profile manager. You can move a profile anywhere you want (except for the Thunderbird program directory) as long as you somehow update profiles.ini. If you're willing to give up the ability to use the profile manager you can use the command line arguments originally added for USB drive support to tell Thunderbird the location of the profile you want to run. In that case, it doesn't matter whether profiles.ini knows about the profile.
Normally all of your messages are stored within the profile. However, its possible to change where each account stores its mail and/or your Local Folders directory to a location outside of the profile. If you use a global inbox for one or more accounts its mail is stored in the Local Folders directory.
Sharing a PC
If several users share a PC and they don't want to see each others mail they should each create their own profile. If they want to share some, but not all of the mail the best solution is to have separate profiles, but configure the Local Folders directory outside of the profile. They could use message filters to automate copying or moving new messages to a folder in the Local folders directory.
If several users with their own operating system account want to share a profile its recommended you move it to a common location that doesn't depend upon the operating systems account name. Each user could create a separate shortcut per this article to run Thunderbird using a specific profile if they use more than one profile. While you only need to physically move the profile once, you need to follow the instructions for moving the profile for each user in order to configure their copy of profiles.ini to point to the profile.
If each user has their own PC you could store the profile on a file share. Thunderbird supports both drive letters and UNC pathnames when specifying the location of a profile. The file server will lock access to the files as needed to prevent corruption when multiple users access the profile at the same time. However, due to the way Thunderbird works there are problems having multiple users access the same folder at the same time. It works best if all of the messages in that folder have already been read and each user just reads messages in that folder.
Most file sharing software only allows one user to have write access to a file at a time. Thunderbird uses a separate file to store the messages for each folder and another file to cache the folder listing information for that folder. This means every time somebody reads a new message, changes a label or replies to a message it will lock one or both of those files. This makes it awkward for multiple users to access the same folder at the same time. Thunderbird also writes to the prefs.js file whenever it exits, even if you didn't change any settings.
Some users appear not to have any problems sharing a profile on a file share, while others find it unusable. This appears to be due to differences in how they share the profile. Its best suited for multiple users who don't access the profile at the same time or a single user who uses multiple PCs.
Windows Terminal Server
There aren't any known issues with using Windows terminal servers.
You can store both the profile and Thunderbird on a file share. The only file that has to be on the PC is the profiles.ini file used by Thunderbird to tell it where the profile is stored. However, if you use Portable Thunderbird you can use command line arguments to specify where the profile is stored instead. The main disadvantage of Portable Thunderbird is you can't use the profile manager and new releases aren't available as quickly.