Hybrid query with Exchange 2019

[whatwaht]

Hey all,

We have 2x Exchange 2019 CU13 in a DAG.  We are looking at going hybrid (full) but won't be migrating any mailboxes in the near future.

Two things:

We use Teams, and I read that Modern Hybrid doesn't support Teams accessing calendars with on-premise mailboxes?  Is this still the case and mean we have to use Classic Hybrid if we want that functionality?

With Classic Hybrid it mentions requiring a direct smtp connection between online and on-prem.  We have a smarthost between the outside world and our on-prem for smtp (it does spam/virus checking as well as dkim).  Would we require a second incoming smtp connection for classic hybrid?

thanks

jc

EDIT: we are running Azure AD Connect 2.2.1.0 for our AD sync - everything for AD is managed on-premise.

[#2]

As we don't have any online mailboxes and are not intending to have any in the near future, can we still run the hybrid wizard (ews is internet accessible) and make sure we enable Centralised Mail Transport?

Would this be enough to provide Teams on-premise calendar access (the real goal at this stage) and then we can worry about mail flow later?

[#3]

Hi all, anyone have any advice on my queries?

Just really wondering if we can set Classic Hybrid up without the port 25 communication just to get Teams Calendar integration.

[#4]

Question 1: Yes it remains the same...if you want Teams free/busy, Microsoft advise not to use the modern hybrid agents
Question 2: Yes you would need a direct SMTP route from EXO to your on-prem Exchange server. When you run the hybrid configuration wizard and your MX record still points on prem, the hybrid connector created in EXO is only configured for messages between your EXO mailboxes (which you may have none initially) and your on-prem mailboxes. The reason for this is that messages sent from an EXO mailbox to an on-prem mailbox is considered "internal" and you don't want this mail going via a 3rd party message hygiene service/appliance.

[#5]

No...centralised mail flow is not related to Teams free/busy or calendar access. The problem is that Teams requires direct access to EWS to see a users calendar, and the hybrid agent can't (currently) provide that, so you need a full hybrid which publishes this to the internet so Teams can access the Exchange server directly and get the calendar information.

[#6]

Thanks for the replies@Dan Snape 

If we don't have any EXO mailboxes, can we still set up classic full hybrid without the direct smtp connection, or will the wizard complain that it isn't there and not continue?  EWS will be accessible.

On our primary IP address we already have port 25 open for mail flow to/from our mailscanner appliance which sits in front of Exchange on-prem.  We would need another IP to permit stmp traffic to/from EXO.  We would sort this out when we decide to start setting up EXO mailboxes.

[#7 · Accepted solution]

HCW will throw an error saying the connector from EXO to on-prem couldn't be validated, but will still complete. You can use a separate namespace for the hybrid mail flow (ie hybrid.contoso.com), but that name will also need to be in the certificate on the Exchange server

[#8]

Thanks@Dan Snape 

Luckily for some reason we have 4 dns names on the Exchange certificate (one for OWA, one for autodiscover and two that were unused: one I re-purposed for download domains and one is spare).