Networking question and Exchange SMTP?

Hello all.  Ok I need a little knowledge here about how this is setup.   We have an external facing web box in-house at one of my client sites.   Also in-house there is an exchange server that supposedly has SMTP setup, not sure how that is setup and would love if someone can explain how this is setup.  Anyway the network guy told me the SMTP host name such as "mail.[domainname].com" which I beleive it the non-authoritive name whatever that means :).   Well the username and password was told to me at the time I did not need it.  Now however I am getting an error when trying to send an email about incorrect username or password etc.    Nothing has changed on my end so I beleive something else changed on the networking side.    First how would an external box access this SMTP server as the host if it is internal?  (Firewall?).  Then if that is the case where would the SMTP setup reside on this exchange server and can a username and password be setup?  Hopefully this makes some sense as I am tying to educate myself on the networking side of things so I can properly battle if need be :).
sbornstein2Asked:
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WadskiIT DirectorCommented:
It sounds like someone has cleaned up the Active Directory and deleted the account that was your From / To Account.

SMTP is part of Exchange and your username and password were the security negotiation toallow you access without making the Exchange Server an open relay.

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sbornstein2Author Commented:
So if there was not username and password, does that mean there was a firewall allow for that box or something possibly and that there was open relay between the two?
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WadskiIT DirectorCommented:
The firewall forwards traffic on Port 25 to the Exchange Server.  This is the port that SMTP uses and therefore the port that email travels on.

ie:

My Mailserver finds your mailserver by looking up the MX record on your domain and then using the top priority one listed.  This will point to your firewall which then IP forwards the traffic to Exchange.

This works by my SMTP server talking to yours and yours accepting the mail because it meets the criteria set out by your System Admin:
1. Mail is TO: someone in the domains listed
2. Mail is FROM: someone allowed to send via this server
3. Server has passed a username and password which it accepts
3. Server is at an IP address allowed to send mail through this server
(for example)


Your webserver may have been specified by IP address, by username / password or allowed due to it only sending mail to an internal email address on the exchange server.  Potentially you may have been using this mailserver as an open relay to send mail out onto the internet. Either way something have changed by the sys admin and this is no longer possible.
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