Two internet connections & one Exchange 2K3 server - Problem?

[pkirill]

We have two internet connections here in the office - a T1 and a cable internet (w/ static IP). The T1 is the "primary" with the cable kicking in when additional bandwidth is needed. Since we set this up, I've noticed an increase in NDR's from recipients like this:

JaneD@recipient.com on 3/31/2008 11:00 AM
There was a SMTP communication problem with the recipient's email server. Please contact your system administrator.
<SERVER.domain.local #5.5.0 smtp;550 authentication required>

It's sporadic and a resend usually goes through fine. I've been telling my users that it's the recipients server, but I'm curious if it doesn't have something to do with our dual connection setup. Both providers have updated our MX records to reflect the proper reverse lookup (mail.domain.com).

So I guess my question is general in nature and it is without making any changes to our Exchange 2003 configuration, can a dual connection cause problems with the way a recipient's server views our email?

Thanks for any help - if you haven't noticed I'm not an Exchange guru...

 

[Zelandakh]

This will depend on how your firewall is set up. I'd say you should look at the MX records for your domain and check that the additional public IP is in there. That may resolve this.