What I have found is that SNAP have blocked access to their email platform from the XT IP Address ranges.
Even if a SNAP customer uses another SMTP server for ending email, SNAP still block this as IPaddress validation back to SNAP is part of the SMTP verification.
An email from an XT customer clearly states that "Snap have insisted that they will not be granting access for anyone who uses the XT Network".
I strongly believe that this is a mis-communication between an over zealous call centre person at SNAP and their customer.
My research indicates that there is only one other NZ ISP also blocking XT access for their customers.
If there is anyone out there who can help it would be appreciated.