An express transfer, in addition to transferring the requested cPanel account(s), performs the following actions on the source server:
1) Updates the account's A record to point to the destination server.
2) Whenever appropriate, changes the domain's nameserver entry to point to the destination server.
3) Updates the mail databases to point to the destination server.
4) Adds a redirect for the Account Moved page (cgi-sys/movingpage.cgi)
5) Blocks SSH and FTP logins to the source server for accounts that were transferred.
In all, if you transfer one account abc.com (from previous IP or server xx.xx.xx.1), the zone file for abc.com on server xx.xx.xx.1 will be altered automatically using IP where the account is being transferred i.e. xx.xx.xx.3
Note:- in this case nameservers are like,
for server xx.xx.xx.1,
ns1.server1.com (xx.xx.xx.1)
ns2.server1.com (xx.xx.xx.2)
for server xx.xx.xx.3
ns3.server1.com (xx.xx.xx.3)
ns4.server1.com (xx.xx.xx.2)
Thus, the domain will start resolving to new IP address - xx.xx.xx.3 using nameservers (ns2.server1.com & ns4.server1.com)
Express transfer option can be seen from option WHM >> Copy multiple account from another server
Ref:-
http://docs.cpanel.net/twiki/bin/view/AllDocumentation/AllFAQ/WHMsFAQ#What is an express transfer?