Forum Discussion
Migrating from MDaemon emails to Exchange online
IMAP only copies mailbox data, so coexistence between MDaemon and Exchange Online requires separate mail routing.
A practical setup is:
- Keep the MX record pointing to MDaemon during the migration.
- Set the domain in Exchange Online to Internal relay, then create an outbound connector to MDaemon. This routes messages for non-migrated recipients back to MDaemon.
- After a migrated user’s final IMAP sync, configure MDaemon to route new mail for that user to their verified Exchange Online routing address, normally an onmicrosoft.com address. Check your MDaemon version’s documentation for the exact forwarding or routing setting.
- Switch the user to Exchange Online and test mail in both directions.
- After everyone has moved, update the DNS records, remove the temporary routing and change the domain back to Authoritative.
Do not create Exchange Online mailboxes too early. Once a cloud mailbox exists, Exchange Online treats that address as local instead of relaying its mail to MDaemon. Also test for routing loops before moving a real user.
Microsoft guides:
- https://learn.microsoft.com/en-us/exchange/mailbox-migration/migrating-imap-mailboxes/migrate-other-types-of-imap-mailboxes
- https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/manage-accepted-domains/manage-accepted-domains
- https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/set-up-connectors-to-route-mail
Hi NathanReed,
Thanks a lot for the info.
The step you mentioned "Migrating users gradually is possible, but mail routing must be planned so messages reach both migrated and non-migrated users during coexistence." that is what I want to achieve as well,
I've migrated on-prem Exchange to EXO, not IMAP, are there any links/ articles? so I can learn more even better step-by-step, that would be appreciated.
Regards
IMAP only copies mailbox data, so coexistence between MDaemon and Exchange Online requires separate mail routing.
A practical setup is:
- Keep the MX record pointing to MDaemon during the migration.
- Set the domain in Exchange Online to Internal relay, then create an outbound connector to MDaemon. This routes messages for non-migrated recipients back to MDaemon.
- After a migrated user’s final IMAP sync, configure MDaemon to route new mail for that user to their verified Exchange Online routing address, normally an onmicrosoft.com address. Check your MDaemon version’s documentation for the exact forwarding or routing setting.
- Switch the user to Exchange Online and test mail in both directions.
- After everyone has moved, update the DNS records, remove the temporary routing and change the domain back to Authoritative.
Do not create Exchange Online mailboxes too early. Once a cloud mailbox exists, Exchange Online treats that address as local instead of relaying its mail to MDaemon. Also test for routing loops before moving a real user.
Microsoft guides:
- https://learn.microsoft.com/en-us/exchange/mailbox-migration/migrating-imap-mailboxes/migrate-other-types-of-imap-mailboxes
- https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/manage-accepted-domains/manage-accepted-domains
- https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/use-connectors-to-configure-mail-flow/set-up-connectors-to-route-mail