I just migrated from Exchange 2007 to 2013. The 2007 server has been decommissioned completely. All is well except for the distribution groups... I can successfully email the groups from my outlook, but if a 3rd party application tries to email those groups the mail never gets delivered. For example..... I have Backup Exec 2014. It is configured to email notifications when the backups are completed.... It is supposed to email a distribution group called ITGROUP. It no longer works. BUT, if I change the recipient address in backup exec to my email address it works. So, it appears that the RELAY portion is working for individual email addresses, but not groups. I am having this issue with multiple 3rd party applications when emailing to groups... And all of these notifications were working prior to the migration.