Is mail still forwarded if there is no trust between the Source and Target?
Exchange Migrator 2.x
Mail fowarding does not rely on the trusts, but rather SMTP. As long as the Source server can still forward SMTP mail, then a trust being up or down is not an issue.
By default Exchange Migrator creates a source custom recipient configured to forward messages intended for the source mailbox to the migrated mailbox. Exchange Migrator copies e-mail addresses from the source mailbox to the source custom recipient. Since the source custom recipient contains the source mailbox addresses, mail intended for the source mailbox is received by the source custom recipient, which forwards the mail to the migrated target mailbox.