Is it possible to set up simultaneous operation of the hoster's mail service and Exchange 2013?

Question

Mail server

I have a question that I can't find an answer to anywhere.
Mail in our organization is stored at the host.
At the moment, we are implementing Exchange 2013, but a dilemma has arisen: a lot of employees are scattered around the country and abroad, and it will not work for everyone to reconfigure email clients at the same time. Is it possible to make a partial transfer of employees to receive mail from Exchange and at the same time so that those who were not transferred could receive mail using the old connection scheme?

Answer 1

I keep forgetting to post the solution.
We expose two MX records in DNS with a priority on Exchange.
In Exchange, we create a send connector with an internal relay.
Further we delete a box from the server of a hoster and we add the same box to Exchange.
Everything is working.

Answer 2

if memory serves (never did, we followed a different migration path), then you can configure your mail domain in exchange not as "Authoritative domain" but as "internal relay"

Answer 3

It is possible through an additional domain. Users will not see it.

Answer 4

it will not be possible to reconfigure mail clients for everyone at the same time

What clients and how are they configured now?
Exactly. How are users working now? Where is the mail? They have it downloaded via POP3, and sent - again, they have it, or what?

Answer 5

Depends on how you have configured Exchange, but you can do this: enable the domain that you use External Relay and create a Send-Connector that will forward mail to the host server. The MX records must point to the Exchange server.
Thus, all incoming mail will go to Ex, it will check the local database and if the user is not there, send a letter to the host server.
PS I saw that the solution has already been proposed. On the host side, you need to create stubs for all mailboxes that are in the exchange server. A stub is a simple forward to an email from another domain (unfortunately, there is no way without it). That is, you add a domain to the exchange - moydomen2.ru and write an additional email to each user with this domain. On the host side, create a forward like [email protected] -> [email protected], where [email protected] is what you wrote to the user in the exchange.
Well, or send everyone instructions on how to remake your profile on a new server ...

Answer 6

No. Send everyone in advance letters about reconfiguration on X-day, block all accounts from the hoster on X-day