That is not right.
your mail server host name is: mail0
domain name is: mail0.ini
Change it to:
mail server host name is: mailserver0 (This is the name that all other VMs must be able to ping the mailserver VM with)
domain name is: mail0.EXTRAPART.mail0.ini
VMware's example domain name is: maildomain0.eng.vmware.com. This has 4 parts, the domain "maildomain0" and mail qualifier "eng.vmware.com". For you this is domain "mail0" and mail qualifier "EXTRAPART.mail0.ini".
Line 2 includes Mailserver0 because it is the form <hostname>.<domain_name>.<mailqualifier_part1>.<mailqualifier_part2>.<mailqualifier_part3>.
Does this make sense?