Exchange Hybrid: 554 5.4.108 SMTPSEND.DNS.MxLoopback
When routing emails in Exchange Hybrid mode, the following error may occur between Exchange on-prem and Microsoft 365 mailboxes when sending mails from a local mailbox (or an external sender) to an M365 mailbox: Remote Server returned '554 5.4.108 SMTPSEND.DNS.MxLoopback; DNS records for the next hop domain are configured in a loop -> ... Read more
