Mix Office365 Exchange and IMAP/POP3

By | March 14, 2016

Email for a domainname can only be delivered at one location (our Exchange Online emailaccounts or emailaccounts hosted in our webhosting product) since MX records are domain specific and cannot be different depending on the emailaddress (doh ;-)). To avoid complicated setups we prefer to use only one kind of email within a domainname, either Exchange Online (office365) or IMAP/POP3 (webhosting package). However technically it is possible to mix both, you need to take the following steps to do so:

  1. Add the domainname to Office365. Add the autodiscover and msoid records to the DNS of the domainname but do not change the MX records. Skip further DNS verification.
  2. Add new users for the emailaccounts you wish to host in Office365.
  3. Add a secondary emailaddress to each emailaccount you just added, make sure this secondary emailaddress is hosted at Office365 (you can use the default <name>.onmicrosoft.com domainname for example).
  4. On the server that is hosting your email (see MX records) add email forwarders for the emailaccounts you wish to host at Office365. Forward all email for these emailaccounts to the secondary emailaddresses.
  5. All email for these specific emailaddresses will now be forwarded from the receiving server running IMAP/POP3 accounts to the Office365 mailboxes. As a last step we have to configure the mail flow within Office365 to make sure all email send from a Office365 account to other emailaddresses under the same domainname is delivered to the official mailserver and not locally within Office365 (which won’t work since other emailaccounts do not exist in Office365, so you will receive an Error: 550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup).

Go to the Exchange admin center.


Go to “accepted domains” in the Mail flow menu.


Now select the domainname and choose Edit. Set the “accepted domain” radio button to “Internal Relay: Email is delivered to recipients in this Exchange organization or relayed to an email server at another physical or logical location.”.


Save this setting. Email from a Office365 account to other emailaddresses under the same domainname is now correctly being delivered. With these steps you can use Exchange Online accounts mixed with IMAP/POP3 accounts.

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