Outlook RPC/HTTPS dosen't work on LAN but works fine from outside.

Outlook RPC/HTTPS works great when remote, but when on LAN it doesnt connect. Outlook says "Trying to connect......."

When I try outlook /rpcdiag I can see that it tries to connect but fails and then after a while it connects using TCP/IP instead off HTTPS.

AND that is because when on LAN  the PC's can't connect to https://mail.myexternaldomain.com

If I (on LAN) in internet explorer tries OWA using: https://mail.myexternaldomain.com/exchange it fails. But https://myInternalExchangeServer/exchange works fine and from outside the https://mail.myexternaldomain.com/exchange works fine.

So ther is a LAN problem with https://mail.myexternaldomain.com

Tried to run

NSLOOKUP mail.myexternaldomain.com and it answers this and it seems to be the correct answer.

Server:  exchange.mydomain.local
Address:  192.168.22.3

Non-authoritative answer:
Name:    mail.myexternaldomain.com
Address:  my.external.ip.address


SO WHY CAN'T I CONNECT when on LAN????

Maybe this is not an Exchange / Outlook /RPC/HTTPS question but a DNS question.