merging two imap accounts

[nanooq at nanooq.org]

Hello to all,

how do I merge two different IMAP accounts of the same e-mail (as in: I 
switched hosts and redirected my domain name)?

The difference is that IMAP-account (1) on hoster A stopped getting new 
mails by the end of January and a new IMAP-Account (2) was opened on 
hoster B on the first of February. They were both managing emails for 
the same address, therefore I wonder, how to merge the old one into the 
new one.
Without running into an UID validity problem. That's what I get, when 
switching .offlineimaprc from one account to the other.

I am looking forward to your answer.

Thank you in advance,

nanooq