I am trying to configure sendmail (v 8.12.5-7 on Redhat Linux 8) on my server. I am unable to send or receive messages using mail command (or any command for that matter).

My mailserver name: abc.com
I have setup user1 to alias as user1@def.com so that all of his mails are relayed to user1@def.com. When I send a mail to user1@abc.com I can receive it on user1's account on abc.com. but when I send a mail to user1@def.com I get the message on user1@abc.com. why is that so? I am also not able to poll the server for mail from any outside client.
I checked the firewall and the port 25 (smtp) is open.

Please advice....

KS

First, check the configuration with the following:

/usr/lib/sendmail -d0.1 -bt < /dev/null

The output will be something like this:
Version 8.11.6+Sun
Compiled with: LDAPMAP MAP_REGEX LOG MATCHGECOS MIME7TO8 MIME8TO7
NAMED_BIND NDBM NETINET NETINET6 NETUNIX NEWDB NIS NISPLUS
QUEUE SCANF SMTP USERDB XDEBUG

============ SYSTEM IDENTITY (after readcf) ============
(short domain name) $w = host
(canonical domain name) $j = host.mydomain.com
(subdomain name) $m = mydomain.com
(node name) $k = host
========================================================

ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

It may show warnings or errors with the configuration.

Second, please explain the alias you entered - is it as follows?

On system abc.com
user1: user1@def.com

This should tell sendmail to forward any mail for user1@abc.com to user1@def.com. You then have to insure that user1@def.com accepts mail from abc.com (look in your sendmail.cf and aliases files).

Third, check that mail isn't suppose to stay on abc.com according to the sendmail.cf file on abc.com.

1. output from: /usr/lib/sendmail -d0.1 -bt < /dev/null

hostnameVersion 8.12.5
Compiled with: DNSMAP HESIOD HES_GETMAILHOST LDAPMAP LOG MAP_REGEX
MATCHGECOS MILTER MIME7TO8 MIME8TO7 NAMED_BIND NETINET NETINET6
NETUNIX NEWDB NIS PIPELINING SASL SCANF STARTTLS TCPWRAPPERS
USERDB USE_LDAP_INIT

============ SYSTEM IDENTITY (after readcf) ============
(short domain name) $w = myhostname
(canonical domain name) $j = $w.abc.com
(subdomain name) $m = <null>
(node name) $k = myhostname
========================================================

ADDRESS TEST MODE (ruleset 3 NOT automatically invoked)
Enter <ruleset> <address>

Did not get any errors or warnings but... there is $w preceding my domain name. And i notice that there is no SMTP in the compiled with list! Is this why I am unable to send messages to the outside world?

2. Yes the aliases files is as follows:
user1: user1@def.com

3.
>>Third, check that mail isn't suppose to stay on abc.com according to the sendmail.cf file on abc.com.

How can I check this?

Check on the def.com system that user1 gets email sent from def.com. This will insure any email coming into def will not be sent somewhere else.

On def, send mail to user1. The best way to do it is by running sendmail in verbose mode (normally $ /usr/lib/sendmail -v user1 < somefile ) and inputting the contents of a small file as the body.

Look for the the following in your sendmail.cf files on both servers.

# "Smart" relay host (may be null)
DSmailhost.mydomain.com

# who I send unqualified names to (null means deliver locally)
DRmailhost.mydomain.com

# who gets all local email traffic ($R has precedence for unqualified names)
DHmailhost.mydomain.com

# who I masquerade as (null for no masquerading) (see also $=M)
DMmydomain.com

# class E: names that should be exposed as from this host, even if we masquerade
# class L: names that should be delivered locally, even if we have a relay
# class M: domains that should be converted to $M
CL root oncall bkops
CE root


You will note that the Class L will tell the server to keep root, oncall, and bkops email on this server. All other email is forwarded to mailhost (a CNAME in DNS which can be set to whichever server is handling email). At some point, if all your email is strickly UNIX based, the server that gets the email must know about all the different users (they must be real accounts in /etc/passwd) or sendmail will send back the message as undeliverable.

Also insure your postmaster email is going to a real account. Messages that bounce will eventually show up there and it's a good way to figure out what may be wrong - also check your messages file or log files

Thanks... I had not configured my domain properly. It is working now.

Great posts RTM. Thanks for the great work. Neo