Hello all! I hope someone can help me out here...

We've a Sendmail box running along just fine with a single NIC and Sendmail configured to bind to it with a routable IP. All is well with the config...our users are able to send and receive without any issues.

Now to the "how do I configuration"...I have another NIC in the server and I've also configured it with a routable IP on a totally different Class C block and I've configured Sendmail to bind to it as well using the following:

define(`confDONT_PROBE_INTERFACE', `True')dnl
...
FEATURE(`no_default_msa')dnl
...
DAEMON_OPTIONS(`Port=smtp,Addr=64.X.X.X, Name=MTA')
DAEMON_OPTIONS(`Port=smtp,Addr=204.X.X.X, Name=MTA')

The intention is redundancy in case one or the other IP blocks go offline and I want to use a single server.

I've two MX records set up with different priorites. For example:

mydomain.com. IN MX 5 mail
mydomain.com. IN MX 10 mail2
mail.mydomain.com. IN A 64.X.X.X
mail2.mydomain.com. IN A 204.X.X.X

I have two routers (Cisco 3640's) that correspond to each Class C block and eth0, eth1 are both configured to use the correct gateway.

When I save/rebuild my M4 config and use dnsstuff.com to check my DNS configs both of my IP's configured in the MX records successfully respond to a SMTP request...HOWEVER...our users that are using a mail client configured with an SMTP server of mail.mydomain.com can NO longer send email. What gives? I've spent hours on this and I have obviously tried everything that I can think of. Is this DNS related OR Sendmail related? HELP!!!

sounds DNS related

but i have noticed that sendmail will use the default route on the box to send. binding it is just for listening, and since you want it to listen on both interfaces, you really don't need to define it.

so if your eth0 is the primary nic that probably has the default route, so when it goes down, sendmail doesn't know where to send.

Thanks....But my customers can't send even when the default route is accessible per the aformentioned setup. Depending on the mail client they get a message like "connection was interrupted". Any ideas??

are you using ssl or sasl?
if so you need to disable the email scanning on your antivirus because it can't scan encrypted mail

also when you type
hostname
make sure it types out what your domain is like domain.com

No encryption whatsoever...I'm at a loss....for days now. 'hostname' ouput is correct. Any more ideas greatly appreciated.