NAT Incoming SMTP Traffic to an SMTP Server

If you only have one public IP address, or a very limited number, you can create a network object NAT rule that translates inbound traffic, bound for a static IP address and port, to an internal address. We have provided procedures for specific cases, but you can use them as a model for other supported applications.

Before you begin

Before you begin, create a network object for the smtp server. For the sake of this procedure, we will call the object, smtp-object. See Create Network ObjectsCreate Network Objects for instructions.

Procedure

Step 1

In the left pane, click Security Devices.

Step 2

Click the Devices tab to locate the device or the Templates tab to locate the model device.

Step 3

Click the appropriate device type tab.

Step 4

Select the device you want to create the NAT rule for.

Step 5

Click NAT in the Management pane at the right.

Step 6

Click > Network Object NAT.

Step 7

In section 1, Type, select Static. Click Continue.

Step 8

In section 2, Interfaces, choose inside for the source interface and outside for the destination interface. Click Continue.

Step 9

In section 3, Packets, perform these actions:

  • Expand the Original Address menu, click Choose, and select the smtp-server-object.

  • Expand the Translated Address menu, click Choose, and select the Interface.

  • Check Use Port Translation.

  • Select tcp, smtp, smtp.

Step 10

Skip section 4, Advanced.

Step 11

For an FDM-managed device, in section 5, Name, give the NAT rule a name.

Step 12

Click Save. The new rule is created in section 2 of the NAT table.

Step 13

Review and deploy now the changes you made, or wait and deploy multiple changes at once.

Entries in the ASA's Saved Configuration File

Here are the entries that are created and appear in an ASA's saved configuration file as a result of this procedure.

Note

This does not apply to FDM-managed devices.

Object created by this procedure
object network smtp-object
host 10.1.2.29
NAT rule created by this procedure
object network smtp-object
nat (inside,outside) static interface service tcp smtp smtp