Configuring Sendmail as a client only, how?

We are running sendmail-8.13.4 on AIX.

I need to update the configuration and make sendmail act as a relay client only, meaning it will only be used to send mail out of the host and NOT accept mail.

Here is my client.mc config:

include(`/usr/samples/tcpip/sendmail/m4/cf.m4')
VERSIONID(`sendmail config for aix7')
OSTYPE(`aixsample')dnl
MASQUERADE_AS(`myserver.com')dnl
FEATURE(`masquerade_envelope')dnl
FEATURE(`accept_unresolvable_domains')
FEATURE(`accept_unqualified_senders')
FEATURE(always_add_domain)dnl
FEATURE(`nullclient',`mail-relay.xxxx.myserver.com')dnl
define(`STATUS_FILE', `/etc/mail/statistics')dnl
define(`MAIL_HUB', `myserver.com.')dnl
define(`LOCAL_RELAY', `myserver.com.')dnl

We have an MS Exchange server, so we are basically using sendmail on a particular AIX host to forward all email to the exchange server and let Exchange handle everything.

The above configuration works fine for sending email to recipients using:

mail user@myserver.com

What I also need to do is be able to send the email with only specifying the alias part and not the domain, so if I do:

mail user

** sending email to userid, omitting the @myserver.com recipient domain part

I want sendmail to append the @myserver.com in this situation where a domain is not given. Is this possible without maintaining some sort of alias/list file for every possible userid > userid@mydomain.com?

Thanks.

Are you using 'mail' or 'mailx' from the command line, or are your outbound emails essentially program error or status messages?

I realized my original question was very confusing, updated to be specific at the issue I am stuck at. We are using the "mail" command included in AIX.

Why not simply create your own version of mail.

user=$1
echo $user|grep @ >/dev/null
if [ $? -ne 0 ]
then
    domain=ourdomain.com
    /usr/bin/mail $user@$domain
else
     /usr/bin/mail $user
fi

Put your version of mail ahead of the system version in your PATH.

Our programs and 3rd party programs call the "mail" program directly, so I would need to rename /usr/bin/mail to something else, create my script and call the renamed mail.

Is there a way to do this in the sendmail config (possibly via their very confusing rewrite rules?) so to avoid messing with system binaries.

You don't need to change or rename any system programs.
Assuming that your application programs call 'mail' and not '/usr/bin/mail' then:
In your user .profile change the PATH statement to include '/usr/custombin' first.
Put your version of mail in /usr/custombin.
This seems significantly simpler than working with the sendmail configuration.