I had the same problem with IMAP and POP3 after installing CU13. It seems like a bug.

I bet if you run Get-ServerComponentState , you see ImapProxy or POPProxy Inactive.

If you can turn in active by this, but it will still not help (Set-ServerComponentState -Identity -Component ImapProxy -Requester Functional -State Active ) or (Set-ServerComponentState -Identity -Component POPProxy -Requester Functional -State Active )

You have to edit registry…

IMAP Setup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ExchangeServer\v15\ServerComponentStates\ImapProxy
there will be two keys:

1) Functional – it must be changed from 1:0:xxx to 1:1:xxx

2) HealthApi -it must be changed from 1:0:xxx to 1:1:xxx

Then restart IMAP services and try to run Get-ServerComponentState, imapproxy should run now.

POP3 Setup:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ExchangeServer\v15\ServerComponentStates\POPProxy

there will be two keys:

1) Functional – it must be changed from 1:0:xxx to 1:1:xxx

2) HealthApi -it must be changed from 1:0:xxx to 1:1:xxx

Then restart POP services and try to run Get-ServerComponentState, popproxy should run now.

If you don’t have all of this registry keys, don’t worry just change the one you have.

Hope it will help.