What do you mean by "address file"? The Address Book?

What do you want to do with the file(s)?

Address books are stored in files with a .mab extension, in your profile.

https://support.mozilla.org/en-US/kb/profiles-tb

If you're thinking about backup and protection of your data, it is probably better to backup the entire profile.

Backing up is important, but not of much use if you can't restore the data. Standalone mab files are not very useful.

Thanks. I had some file corruption of the outboard had drive where I keep a mobile version of Tbird. Restoring things got messy, so I am trying sort out what is where. The server settings when it is running point to the outboard drive, but it tells me that it is using an address book on C. While I can move it over to G, how do I tell it to look there in the future?

So, are you using Portable Thunderbird? If so, your question might be better addressed to a support site for that specific version.

http://portableapps.com/support/thunderbird_portable http://portableapps.com/forums/support/thunderbird_portable

Your data are stored in your profile. By default, in a "regular" installation of Thunderbird in Windows, this is located under Users/<username>/AppData/Roaming/Thunderbird. I understand that in Portable Thunderbird this will instead be located on the portable drive.

It is possible, inside the account settings, to set individual mailstores to be stored elsewhere, using the "Local directory" setting. I usually advise against using this feature as it leads to your profile becoming fragmented and stored in multiple and disconnected locations, making backup and maintenance much harder than it need be. I can't see any sense in using Portable Thunderbird and then deliberately overriding its preferences for data locations.

Regardless of where you put your mailstores, your address book data files (*.mab) will remain in the profile. For this reason, if I wanted any email-related data to be stored somewhere other than the default location, I'd relocate the entire profile and not just the mailstore files. Note that you must leave the file profiles.ini in the mandated location; that's under AppData...Roaming in a default set-up, and I'd expect somewhere on the portable drive in Portable Thunderbird.

Here is an article about the profile and where to find it in regular Thunderbird:

https://support.mozilla.org/en-US/kb/profiles-tb?esab=a&s=profiles&r=1&as=s

But if you're using Portable Thunderbird, this should instead be on your portable drive.