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Step-by-Step Configuration and Troubleshooting Best Practices for the NGFW, NGIPS and AMP Technologies A Visual Guide to the Cisco Firepower Threat Defense (FTD)
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ASA 5520

My device has 3 interfaces configured: inside, outside, DMZ.  Right now I can access the Mail server from the Internet using domain name which is on DMZ interface. The issue here is when users  they need to configure their Ms Outlook for Incoming mail server & outgoing mail server  FQDM e.g ( the ms outlook failed to connect , but when using its internal IP address which is Mail server IP address its working fine. Are there any special statements I need to add to the ASA such as nat or ACLs to make this work?  My LAN is and DMZ is And My Mail server IP address is 

Hall of Fame Super Silver

The best way to remedy this

The best place to get firewall questions answered is the firewall forum.

However, the way to remedy this problem is to setup your DNS server so that it returns the address when resolving the FQDN for internal clients. If that's not an option, then you could deploy a host file to them that statically sets it.

You could also put in a NAT rule that tells inside clients trying to hit the mail server public address to instead use the DMZ address but that's a bit of a hack.

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