IMAP on Exchange server SSL issue

I am trying to setup IMAP access to my Exchange server 2016.

Followed these instructions

And I see this

[PS] C:\Windows\system32>Get-ImapSettings | Format-List *ConnectionSettings,*Bindings,X509CertificateName

InternalConnectionSettings : {ex-sx-01.domain.local:993:SSL, ex-sx-01.domain.local:143:TLS}
ExternalConnectionSettings : {exchange.domain.ch:143:TLS, exchange.domain.ch:993:SSL}
UnencryptedOrTLSBindings   : {[::]:143, 0.0.0.0:143}
SSLBindings                : {[::]:993, 0.0.0.0:993}
X509CertificateName        : wildcard-domain.ch

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Which seems to be ok

However if I try to connect I get

MBP13:~ alex$ telnet exchange.domain.ch 993
Trying 000.000.210.252...
Connected to exchange.domain.ch.
Escape character is '^]'.
* BYE Connection is closed. 14
Connection closed by foreign host.
MBP13:~ alex$ 

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MBP13:~ alex$ openssl s_client -connect exchange.domain.ch:993 -crlf
CONNECTED(00000005)
140736108229576:error:140770FC:SSL routines:SSL23_GET_SERVER_HELLO:unknown protocol:/BuildRoot/Library/Caches/com.apple.xbs/Sources/libressl/libressl-22.50.2/libressl/ssl/s23_clnt.c:565:
---
no peer certificate available
---
No client certificate CA names sent
---
SSL handshake has read 7 bytes and written 318 bytes
---
New, (NONE), Cipher is (NONE)
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
---
MBP13:~ alex$ 

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It would seem that my SSL setup is not correct ?!

Any suggestion / pointer ?