I recently moved through a migration of changing my organizations email from .com to .org. All email is working from external to internal and email is being accepted to the users new .org email and through recipient policy, still being accepted through the .com email as well. On occassion, and not every time, when a user forwards an email or sends an email internally, they sometimes recieve the error "The message could not be delivered because the recipient's destination email system is unknown or invalid. Please check the address and try again, or contact your system administrator to verify connectivity to the email system of the recipient."
This is sending email internally and I have verified that the GAL is being updated correctly and at 3 times throughout the day. Any other suggestions on what it could be?