How to set up 2 Exchange in one organization?

Question

Domain Name System

Good day!
I will briefly describe the situation, a little chaotically, but I will try to be as complete as possible:
- there are 2 offices (united via VPN)
- there are 2 domain controllers, one in each location (common domain)
- there are 2 Exchanges, one for each location (in the database of each only those users who are in this location are stored), each of the servers has all the roles
- in each of the locations there are at least 2 IPs (from different providers)
- in the local office network everything works by autodiscovery and connects where
necessary I - inherited :) (if anything, I'm not a big specialist in Exchange).
From what I read, I realized that it might somehow save DAG, but I'm not sure if it's right to use it in my situation.
Question:
If there is no connection in one office (exactly in one), the connection to the local Exchange is lost for clients in this office, and when it is resumed, everything is restored, although the server is active and does not fall - access from outside at this moment works fine, it receives mail from outside.
How to set up automatic external access for Outlook clients and others on mobile devices (iOS, Android)? Although (outside) mobile devices work (with automatic configuration, they only get to one location via autodiscovery), you can manually register the 2nd location (everything works too) - how to win this, there is an idea with DNS RR (but after I figure out the external Outlook connection -clients)
Before writing, this was read:
habrahabr.ru/post/140687
habrahabr.ru/post/139591

Answer 1

I 'm
also puzzled by a similar question
... /12/ow...

Answer 2

1. If there is no connection in one of the offices
It is very similar to the fact that in one of the offices the local DC does not have the role of GC, although I may be wrong, it still looks like there is simply no one to authorize users if the VPN channel to the GC falls.
2. There must be different External URLs for two different locations - ie. when the client connects via autodiscovery - the Exchange that responds - will know in which database the user's mailbox is located, and will give the correct URL to the client.
PS
DAG is, in principle, a necessary thing, but in your case it will not solve the problem. But for that it will solve the problem of mail backup if one of the Exchange suddenly fails - the passive copy will lie neatly on the surviving resource =)
In general, the task is complex, I wrote all my assumptions.

Answer 3

1. GC - was enabled on both DCs (checked), but both DCs and GCs were specified in the Exchange settings. Having registered statically the one in the GC location directory - sort of corrected the situation - left one to see how it will "run" further when people come out after the holidays.
2. That's why it's not entirely clear - there are several connection options - Outlook, OWA, ActiveSync (mobile devices). C Outlook - checked - connects to a "foreign" server outside normally and even works - it should not forward somewhere - it acts as a la "proxy". Regarding OWA - here I agree - it forwards to the right location (there really is a redirect here). ActiveSync - just like Outlook, it doesn't care what "proxy" to work with - this has already been checked too.
How to correctly register autodiscovery for both locations then - I’ll never know, the only thing to somehow separate OWA and MAPI + ActiveSync is ooooh, by the way, this is a good idea, you can also configure your URLs for each one!
DAG - with him just like that - I thought to have a type of backup database on each of the Exchanges - but it will not completely solve the situation for me.