Sendmail not sending mail out from server anymore

I have an IBM AIX Unix server that runs my companies member database.  One of the functions is that it will email members reciepts when the sign up for programs online.  Previously, everything worked fine.  People registered, and then got their reciepts in their email.  Lately, some members have been complaining that they never recieved their reciepts.  We contacted the vendor of the software and they took a look at the system and later responded that sendmail was to blame.  They recommended I do "sendmail -v <email address>".  The result of the command is shown in the code window.  Previously, it only listed smtp.secureserver and mailstore1.  However our domain uses server, so I added that to the list of MX records with a priority of 10 and changed the other two to 20 and 30.  That change netted result shown.  I am wondering if it is due to port settings?  Is sendmail using port 25 to send the mail?  I know that when configuring outlook for employees we use for outgoing server and use port 80 (not the default 25) for the port.  I tried going into and adding the line:

"O DaemonPortOptions=Port=80"

which did not help...

Any suggestions?
# sendmail -v                                       
.                                                                       Connecting to via esmtp
...                                                                     Connecting to via esmtp...
                                                                        Connecting to via es
mtp...                                                                  Deferred: Connection refused by                                                                     

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Where is this AIX server located in relation to the other servers? I know the machines are hosted at godaddy, is that where you host this AIX server too? Are these receipt emails going to people at your domain or external domains? Does this AIX server deliver mail directly or use a smarthost (like one of those godaddy mail servers)?
dumpsterdivingdaveAuthor Commented:
The AIX server is located at out main site.
The reciepts are going to email addresses both inside and outside of the organization.  Most of them go outside of the organization.
To my knowledge, the AIX server does not deliver any mail directly.  The sendmail is only used to get the reciept to the godaddy hosts where their servers then deliver the message to the correct domain/person.
dumpsterdivingdaveAuthor Commented:
It ended up being the firewall that started to block port 25 for some reason.  After re-configuring, sendmail is now sending emails....  Including the 3900 or so that have been backed up for the past month.

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