troubleshooting Question

Cisco NAT/ SMTP Configuration with Overload?

Avatar of aktharchowdhury
aktharchowdhuryFlag for United States of America asked on
13 Comments2 Solutions1607 ViewsLast Modified:
I have a new Cisco 2811 series router, and I need to make sure the email flows through on the right IP both inbound and outbound to ensure that email will not be rejected by domains doing reverse lookup.

So here's the basics:

fastethernet0/0 outside -
fastethernet0/1 inside -

mail inside -
mail public -

I've included what I've got in the router now.   My question / concern is - when email is sent from the inside to the outside internet - will it show as being from the router's .1 ethernet address instead of the .21 address?

Do I need to put an IP nat pool with an access list into place and what would that look like?

Also, should I configure the router for IP Overload?  Figuring 50-100 users on the internal network.
interface fastethernet0/0
description - INTERNET OUTSIDE
ip nat outside
interface fastethernet0/1
description - INSIDE NETWORK
ip nat inside
ip nat inside source static tcp 25 25 extendable
Jody Lemoine
Network Architect

Our community of experts have been thoroughly vetted for their expertise and industry experience.

Join our community to see this answer!
Unlock 2 Answers and 13 Comments.
Start Free Trial
Learn from the best

Network and collaborate with thousands of CTOs, CISOs, and IT Pros rooting for you and your success.

Andrew Hancock - VMware vExpert
See if this solution works for you by signing up for a 7 day free trial.
Unlock 2 Answers and 13 Comments.
Try for 7 days

”The time we save is the biggest benefit of E-E to our team. What could take multiple guys 2 hours or more each to find is accessed in around 15 minutes on Experts Exchange.

-Mike Kapnisakis, Warner Bros