Besides "Amen" to Nathan's response, I'll add my two bits ...

When converting/merging lists, it is possible that multiple addresses
(either exactly the same (except for case), or variations in userid or
node) will be added.  Likewise, some of those mailboxes might end up in
the bit-bucket.  Finally, none of those addresses might be the exact one
that the user is currently generating FROM:s from.

Thus, you can re-incarnate your list with well-known and opted-in
addresses by letting the users subscribe themselves ... just give them
good instructions.

/Pete