How does DMA handle creating the UPN name?
Domain Migration Administrator 6.x
Domain Migration Administrator 7.x
When Domain Migration Administrator migrates a user account to a Windows 2000 domain, the product updates the user principal name to reflect the new domain name. Domain Migration Administrator enforces the uniqueness of the user principal names. If the new user principal name is already being used in the target domain, Domain Migration Administrator appends a number to the name portion of the user principal name, incrementing the number until a unique name is found.For accounts migrated from Windows 2000 source domains, Domain Migration Administrator replaces the domain portion of the user principal name with the DNS name of the new domain. If the account is renamed during migration because of collision handling or global prefixes and suffixes, Domain Migration Administrator adds the new string to the user principal name. For accounts migrated from Windows NT domains, Domain Migration Administrator sets the user principal name using the SAMAccountName@dns‑domain‑name format. (where dns-domain-name is the fqdn of the target domain specified during the migration). It will not apply an alternate UPN suffix, even if it is defined in the target domain settings.
Please note that this information can also be obtained from Appendix C of the product User Guide Under the heading 'How DMA handles User Principal Name (UPN)'.