I'm looking to move some mailboxes to the Office365 exchange plan, however I also need to keep existing POP3 accounts.

Option 1: Is there a best practise for this setup? Do you simply allow Office365 to send from the domain, whilst keeping the old mailbox as a forwarder to the Office365 one?

Option 2: Or do you look to go the other way round, point the MX records to the Exchange server, and then have forwarders on that to a proxy domain to the old POP3 mailboxes?

I'm leaning towards option 1 myself, but open to any more ideas.

Edit to add: There's two domains, a .com and a .co.uk with the .co.uk aliased as a CNAME to the .com so essentially they're the same.

The current POP3 mailboxes are all on the .com domain but receive email from both the .com and .co.uk as you'd expect.

Currently, I just need to move one POP3 mailbox to the Exchange (Office365) setup. I could keep the domain setup "as is", and use the Office365 mycompanyname.onmicrosoft.com as their login, and use either POP3 collection or mail forwarding from the POP3 account.

I'm concerned that messing around with MX records too much could cause more headaches in the future with a split setup. I appreciate that the usual setup is one domain per MX destination.

  • Do you mean that the existing POP accounts should continue to receive new email at the provider they're currently hosted with? – joeqwerty Apr 17 '14 at 12:41
  • Ideally, yes. That way all the users do not need to setup their basic mailboxes again with new addresses and credentials. – RemarkLima Apr 17 '14 at 12:46
  • That sounds like a pretty cumbersome plan just to avoid a few minutes of inconvenience for the users. Maintaining email service for two different providers, maintaining email clients for two different providers, troubleshooting the inevitable I didn't get my important email or they didn't get my important email... it all sounds like a recipe for a nightmare. – joeqwerty Apr 17 '14 at 12:50
  • Very true - however, there's no providers that seem to provide both hosted exchange mailboxes and POP3 mailboxes via the same MX records... Or none I've found based in the UK. I have unlimited POP3 mailboxes through one account already, but no exchange. And all the Exchange accounts are just that or the office 365 kiosk accounts, but they're not cheap for what they are. – RemarkLima Apr 17 '14 at 12:54
  • Is your existing mail server Exchange for those POP3 accounts? Where do the POP3 accounts currently reside? I see your tags but want to be sure before I answer. – TheCleaner Apr 17 '14 at 12:58

OK, I think I know what your setup is, but still a little fuzzy, I still can't tell if you have an existing Exchange server or not. Unless you keep referring to O365 as "Exchange" which is better stated as either O365 or "Exchange Online" to prevent confusion.

so I'll go with this:

If you point the MX records for the domain (@domain.com) to O365, then you'll need to allow it to an internal relay any user's mail that isn't on O365. This is easy enough: Manage accepted domains in Exchange Online | technet.microsoft.com

However, with only 1 user, it seems pointless, and I'm not sure what the licensing requirements would be for such a setup.

The alternative is the other way around...if your POP3 provider allows it. Bringing email for the domain in there and then relaying for that 1 O365 account over to O365.

These relay options are the best choice to allow for interop and expansion later.

The "cheap" alternative is mailbox level forwarding. This would involve having the O365 account stay with the onmicrosoft.com mail address and then have their POP3 account forward to their onmicrosoft.com account. However, it gets tricky when it comes to SENDING from that account unless you don't care that mail coming from that account will be sending as onmicrosoft.com.

Does that help?

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  • Thanks for the info, pretty much what I was thinking and just nice to get confirmation that a) I'm not mad and b) it's a workable way. I think even if I use the .onmircosoft.com address, I can still register the normal domain with O365, send from it and just not have the MX records point to it, then have mail delivered to the .onmicrosoft.com domain. – RemarkLima Apr 22 '14 at 10:07
  • Yes, I believe you are correct. It will let you validate the domain with just the TXT record, so no changes to the MX record will be required. However, you'll need to make sure it is setup as an internal relay at that point, otherwise email from that user to others at your domain will bounce if it doesn't find a local O365 mailbox. See the link for that info, same applies. – TheCleaner Apr 22 '14 at 12:58
  • Thanks again, nice to have the idea validated. If / When it happens I'll post back the results – RemarkLima Apr 22 '14 at 13:23

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