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Using Exchange Online for dual delivery Exchange emails boxes and Gmail inboxes

Currently use Office 365/Exchange Online for email. Domain examples: mydomain.org/mydomain.onmicrosoft.com
Added GSuite to our offerings, but did not enable gmail functionality. Same domain: mydomain.org
Two different mindsets from users: Some want to keep using Exchange Online for email, some want to use Gmail for email. There is no "Definitive Line" where we could logically seperate those users.
Moving away from Exchange Online represents a large number of unwanted changes.
Preliminary research indicates we can use Dual Delivery routing to use an external server to Gmail and Exchange. Does this mean we can just have one Email management system, in this case--Exchange Online--copy emails to gmail, without having to setup seperate, new email addresses on Gmail?

The quote below is taken directly from https://support.google.com/a/answer/2685650

You set up dual delivery to deliver email messages to 2 or more inboxes. For example, users can receive messages in a Gmail inbox and a non-Gmail inbox, such as a Microsoft Exchange inbox or an archiving server.

With this configuration, incoming mail is delivered to a primary mail server, which processes and delivers each message. The primary server then forwards a copy of the message to a secondary mail server, which delivers it to the second inbox. The primary server is the mail server identified in the MX records for your public domain.

If the external server is the primary server, you configure that server to also forward messages to Google. You also configure the Inbound gateway setting in so that Gmail knows that the incoming mail is being rerouted to it from the external server and performs the appropriate SPF checks.

So what I'm seeing is that in order to do this, Exchange Online would be setup to forward messages to Google. Does anyone know what that would translate to on the O365 side? Would that be a connector? A transport rule? An Accepted Domain?

Vasil Michev (MVP)

The problem is that your MX record can only point at one place. Thus if you want to "share" it between services, mail delivery becomes problematic, and sending even more so. In general you can use the "service" addresses (user@tenant.onmicrosoft.com) as a way to avoid the complexities of sharing the same namespace. You can also set up some form of forwarding, either a "regular" forwarding or via a transport/inbox rule, in order to send copies of the messages. In general though, this is not a configuration you should aim for or use as an end state.

There are some basic instructions here: https://support.office.com/en-us/article/domains-faq-1272bad0-4bd4-4796-8005-67d6fb3afc5a?redirectSourcePath=%252fen-us%252farticle%252fPilot-Office-365-with-a-few-email-addresses-on-your-custom-domain-39cee536-6a03-40cf-b9c1-f301bb6001d7&ui=en-US&rs=en-US&ad=US#bkmk_pilot

masnrock

Two different mindsets from users: Some want to keep using Exchange Online for email, some want to use Gmail for email. There is no "Definitive Line" where we could logically seperate those users.

I would literally be asking why you'd want to even give this choice. Management is going to be FAR easier keeping all users in one mail system. You're going to end up with a large number of limitations right off the bat, and you're definitely going to hear users complain about it. I guarantee you'd eventually get requests like "I like Gmail, but I'm missing x feature that I had before", then it will turn into "I have to have x feature" (Vasil's link even points out several limitations)

Usually the reason you'd mix systems like that is for testing, maybe even during a migration.

If you need a business reason to go against doing something like that, bring up limitations, complexity, and the increase in costs (running 2 mail systems, supporting 2 mail systems, and complexity. I haven't even touched that topic that I'm sure even both Microsoft and Google would recommend against that kind of arrangement.

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Jian An Lim

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Gopi Raju

As the previous experts mentioned its not a good idea to have 2 email service providers for a single organization users as it may lead to unwanted issues in future, but however You can achieve this using Connectors, lets say example.com is for Office 365 and Example.us is for Google, first add the domain which is for google as a sub domain(Internal Relay) on Office 365 and then configure the connectors. Below is the article which can explain more about this.

https://social.technet.microsoft.com/wiki/contents/articles/36118.configure-email-coexistence-between-office-365-google-apps.aspx