SMPT settings - new email server and relays

We upgraded our email system from Novell Groupwise to MS Exchange a couple weeks ago.  This matters because our moodle instances push email to a number of places.  Each of our moodle instances have a configuration and know about our internal email server, settings ect.

Site admin | Plugins | Message outputs | Email

After the switch from Novell to MS, the moodle instances stopped sending email.  I found out about this when a student informed our help desk that they were not able to reset their password.  Translated, moodle was not sending an email to the students email address with the reset password link.  Upon investigation, I discovered that it was true!  Imagine that.  I verified this by viewing the moodle logs and seeing the SMTP related errors in each of my moodle instances. The SMTP settings needed updating.

I worked with our networking team and had some initial success.  We tested using an internal account within our domain and the server pushed the email to an .  When I tested with an external account - outside our domain, it continued to fail.

I posted a note to a moodle forum about the issue and was informed that there was not really a setting in moodle that needed to be changed as a result from migrating from one SMPT server to another and that I should get that information from the mail server admin.

To help the email server admin understand that the problem was not in moodle, I did a couple testing using the Windows utility Telnet.  I opened up a command prompt and created a Telnet session to test if the server was sending receiving mail, outside of any knowledge of moodle.

It took me a couple tries to get this to work as advertised, but eventually, I was able to prove the server was not able to relay the message from the moodle server.  This helped my co-worker see that the IP address of the moodle servers, all four of them, needed to be added to the relay mail server.

I has another person help me word the request that I send to my email server admin.  "The mail relay server needs to know which internal servers it can relay from".

Once those ip addresses were added to the registry of the replay servers, the problem was solved.  Moodle was once again happily sending email messages to valid addresses.

BTW - a couple of the moodle servers really make use of pushing emails to notify teachers when assignments and quizzes have been submitted or taken.

A final analysis -  to help me understand a little more.  A relay is a desirable thing - so a mail server can send email from addresses outside of its own domain.  But the relay cannot be wide open, since spammers will attach it or become a spam injection point.  To close this "injection point" in the server, more specific information is needed, like who are the other servers in the domain who I will accept emails from that have to be send elsewhere?  This does make sense.