But we don't want to disrupt our existing on prem exchange environment. There will be additional migration, smtp and autodiscover traffic. So we want dedicated cas/mbx servers to take the load which are not hosting the on prem mailbox databases.
So we are building additional Hybrid Exchange servers, natting them to a public IP/FQDN (hybrid.mydomain.com), opening firewall ports between o365 and those boxes. I have worked with fewer previously. So wanted to know how many those dedicated servers will
be optimal.
Regards BM
There is no number that is optimal. If you have sized your existing org correctly, why do you think it wont be able to handle hybrid mode? There will not be any increase in autodiscover or SMTP traffic that will be of any consequence. If you were migrating
from 2013 > 2016, would you add more 2013 servers to handle the mailbox moves? No. This is is no different. I dont see the need or point of adding special servers, quite frankly. Really a waste of resources and time.
The existing servers will still be doing all the work since thats where all the mailbox are. You gain nothing by adding more servers for hybrid.
https://docs.microsoft.com/en-us/exchange/server-roles
When configuring a hybrid deployment in an Exchange 2016 organization, you don't have to install any additional Exchange
servers in your existing Exchange organization. Your Mailbox servers coordinate communications between your existing Exchange 2016 organization and the Exchange Online organization. This communication includes message transport and messaging features between
the on-premises and Exchange Online organizations. We highly recommend installing more than one Exchange server in your on-premises organization to help increase reliability and availability of hybrid deployment features.
