Mailboxes migration from cPanel to ISPC stop Outlook from re-downloading all emails

Dear colleagues,

I have tried lot of ways to properly migrate email server from cPanel to ISPConfig.
The mails are transferred OK and it can be accessed through webmail and used.
BUT, outlook, thunderbird or whatever mail client is redownloading when pop3 all the email messages again.
I've been trying to play with UID and change them following a lot of tutorials, but none with success.
(i haven't tried imapsync because of large number of email boxes and shared cPanel account)

1. I rsync or tar.gz the messages from server1 to server2
2. changed the first line in dovecot-uidlist
3. delete and re-index the dovecot.index
Outlook and thunderbird redownload the messages duplicating again

Have any of you succeeded in something similar?
What are the important files for this?

Thanks in advance, for any guidance

 

That's why I'm asking for personal experience of you fellow users of ISPC.
But you said no re-download "SHOULD" be happening.
I guess that also, but the option of cPanel emails migration being a beta, I'm asking from somebody who have done it and has a positive experience to share its case.
If you have done it successfully - then ok, i will continue that way.

 

We're also suggesting IMAP to everybody, but this is a long time pop3 multi-account (some 20 acc) cPanel on shared platform and pop3 accounts installed nearly everywhere, desktops, laptops, moby...

I don't have any official tutorial for cPanel to ISPC with the migration tool, so that's why I'm asking here.
The regular ISPC>ISPC tutorial states that i should install it on the source server, which in the case of this shared cPanel is not possible.

Have you read somewhere a tutorial for cPanel that i can follow?

Thanks for your time and support

 

I would surely do that in parallel, but i would still leave this question open for some enthusiast that has done it by copying and modifying some of the dovecot files.

Many thanks and best regards to you.