User with a mailbox is in source domain, a matching mail-enabled user is in target domain with Exchange 2007 or later. Email to target user is redirected to source, i.e. primary SMTP address and targetaddress attribute of target user are pointing to the source user. Additionaly to an SMTP address, an X500 address is set on the target mail-enabled user. No advanced registry settings are configured for mailbox-enabling. After DSA matches the two users together and mailbox-enables the target user, they get two primary SMTP addresses with different suffxies, one is the source primary SMTP, other the target primary SMTP set by Exchange policy.
CR ST74739 was created, but during investigation it was discovered that this behavior occurs only when default address policy was not applied to the mailbox. No other scenarios have been discovered.
Based on the info above no fix was released for this issue, since it was an environmental issue.
Resolution is to make sure that the default address policy gets applied to the mailbox.