I've replaced the disk drive in my daughter's MacBook after a total disk crash and reinstalled OSX etc.
She had quite a lot of stuff backed up, but not her MacMail address book.
Fortunately our ISP has kept nearly 3000 emails she sent via webmail (when she didn't have the MacBook with her) over the past 2 years.

Reinstating the email account, we have downloaded all the folders from the ISP.
There are now 2 "Sent" folders. One, created by MacMail with the paper aeroplane icon, contains the emails she has sent since the crash, the other, with an ordinary "folder" icon contains the 3000 recovered emails from the ISP server.

We can add the sent email addresses from the MacMail "Sent" folder to the address book via "smart addresses" and "previous recipients", but this is only a few.

I then tried selecting the ISP "Sent" folder and told MacMail to use this as its "Sent". Sure enough the two folders swapped icons, but "smart addresses" and "previous recipients" still only knew about the few emails in the original MacMail "Sent" folder, they don't pick up the 3000 or so.

1) Can I make SA and PR recognise these emails?

2) Failing that, could I copy or cut and paste the 3000 emails from one folder to the other and get it to work? I don't really want to do this but I will if it's the only way.

3) Is there any way of similarly trawling through the received emails (of which there are over 1000 we've managed to recover) and extracting the senders' addresses into the address book?

We could identify each unique email in both folders and, with smart addressing turned on, add them to the address book one at a time, but this would be a long and tedious process.