iBurst have a policy that in order to prevent spam on their systems they have firewalled access to port 25 which is the port that SMTP and mail sending is run on. In order to allow you to send mail they have provided an internal mail server on their network through which you can send mail.

This - however - means that you are at the mercy of their mail system. Additionally - mail through their server can be reject by SPF policies and cause your mail to bounce.

In order to avoid this you should be sending your mail through a Mail Submission Agent or MSA. The advantage of this is that MSA's are run on port 587 and are not subject to the port 25 blocking. You can then rely on the same person who is hosting your incoming mail to process your outgoing mail.

All our hosting packages have built in support for MSA and will function effectively on iBurst internet connections.