SMTP Server Setup

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SMTP Server Setup

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Setting up your OS/390 or z/OS SMTP Server can be a challenge. Fortunately the IBM documentation is fairly good and when that fails the IBM Support is outstanding. The one thing that is not always clear is that the SMTP server will, by default, send all the e-mail that is processes directly to the recipients e-mail server, something that is not always desirable. When it does that there are two challenges

all e-mail that can't be delivered is queued on the OS/390 or z/OS system
some e-mail servers do a reverse lookup on the sending host name which means that if your OS/390 or z/OS system host name is NOT known to the outside world then e-mail that you send to these servers will bounce back to you.

This page describes briefly how to configure OS/390 and z/OS SMTP to route all outgoing e-mail to your existing in-house e-mail server which solves both of these issues,

OS/390:

Find the dataset pointed to by the SYSTCPD DD in the TCPIP started task JCL and make a copy for use in the SMTP started task JCL.
In the copy of (1) comment out the NSINTERADDR statements. These statements are used to define the domain name servers that will be used to resolve host names.
In the SMTP CONFIG data add the IPMAILERADDRESS statement. The syntax is IPMAILERADDRESS xx.xx.xx.xx where the xx.xx.xx.xx is the numeric IP address of the target mail server.

z/OS:

In the SMTP CONFIG data add the IPMAILERADDRESS statement. The syntax is IPMAILERADDRESS xx.xx.xx.xx where the xx.xx.xx.xx is the numeric IP address of the target mail server.
In the SMTP CONFIG data add the statement:

RESOLVERUSAGE NO

SMTP will now forward all mail for which it is unable to resolve the target host name to the server defined in the IPMAILERADDRESS.