ot: migrating TB user's email to new laptop

another OT:

setting up new W10 laptop with TBird:

user has three accounts, several hundred emails on old laptop BUT NO LONGER on server

two of the accounts are on my Dovecot server, one on ISP server

what's best way to transfer local emails:

transfer TBird files laptop to laptop ? or, is there some way to sync old laptop to server, then retrieve on new laptop ?

thanks,

V