Hybrid Exchange - Database server still needed?

[andrejochemsen]

Hi all,

We have an environment with two on prem Exchange servers. It's a hybrid exchange environment.
Both have the Mailbox role, but server A is used for relaying and server B is really a Mailbox server with several databases.
All mailboxes are migrated to Office 365.

I wonder, can i turn off the Mailbox server (hosting the databases)?

Because when i look in the get-messagetrackinglog i see ALOT of traffic. And when i do a format list on some of the messages i see both Server A and Server B in the log.

All traffic is coming from internal printers, applications, and so on. 
I can imagine that when a printer has Server A as SMTP server setup, the printer will send the message to Server A. Server A will check if it can deliver the message to the mailbox and notices a @domain.mail.onmicrosoft.com alias and sends the email to that address, going to Office 365.
Is Server B (mailboxes) used by Server A for the retrieval of that alias to get the message send to Office 365? Is there a possibility to shut down Server B? Or should i make sure all printers and applications make use of an Office 365 server address because i'm able to shut down Server B?

Thanks!

[#2]

what version of Exchange are you running? You can definitely run hybrid with just one server, and it doesn't have to have a mailbox DB. Just be aware that you won't have an redundancy for the SMTP relaying for you devices and on-prem apps. There are some system and health mailboxes that Exchange expects to exist, so generally I'd recommend retaining a small mailbox DB just for these.

[#3]

Hi Dan,
Thank you for your reaction.
Server A seems to be Exchange 2013 (latest CU).
Server B is Exchange 2019.

When i do a get-mailbox on the databases i see several application specific mailboxes and only one Exchange specific mailbox, the DiscoverySearchMailbox. Not sure if that one is important, but it seems like most system/health mailboxes are already gone.

[#4]

By default get-mailbox won't show the system mailboxes. You need to use various switches to see them (arbitration, publicfolder, auditlog, monitoring)