there is no record of when you used it, as I know about. A work around could be to use an add-onEmail Address Crawler Select only messages younger then a year (or what ever) in the SENT-folder(s) Use the crawler on those. Save and move your old addresses into another a-book and move those crawled ones into your main one.

You'l loose all additional data thou.

Well, I don't know how far back the sent mails go. Also, most of them are probably ones I never sent anything to - I think Thunderbird gets the addresses from everything I've received for the collected addresses.

This would be a simple and useful feature to add to the program.

Might so be, hopefully the developers see this, I'm just another user like you.

Well, I don't know how far back the sent mails go. Also, most of them are probably ones I never sent anything to -

The sent- folder is supposed to keep a copy of anything you sent. That is if you set your account up to save a copy of them. (Account settings / Copies & folders )

As they are copies they also contains a time and date. You can set a search-filter to only collect the last year or so. From this you can create a new address-book with the help of the crawler.

I think Thunderbird gets the addresses from everything I've received for the collected addresses.

The collected addresses are supposed to only collect addresses you sent to and you don't already have in your other address books.

On every account settings you can select which address book to use for auto completion

If it's worth the time you can: export your address -book in .csv format and then import it in a spreadsheet. Do the same with your crawled A-book. Set up a rule to create a third sheet were you only copy those in sheet one that are also in sheet two. Import the new creation into Thunderbird