Moving domains from one server to another

[The Guyver]

Hi there,
I need to move some mail domains from one server to another one
the first server runs with vpopmail 4.9.x
(don't remember exactly how do I check the version number?)
while the second runs vpopmail 4.10.35

since the first one had only 6 domains I need to move all of them (including
mails)
to the new one (that runs about 50 domains)

what should I do in order to make the moving less painful for me and the
users?
Thanks in advance to anyone answering.

Best regards,
Guyver