At 04:42 p.m. 15/07/2014, you wrote:
We have had enquiries from several of our customers in the last couple of days regarding an email they have received from Telecom. It relates to a change in Telecom's email service that I find interesting.
These customers use Telecom as their ISP, and have a mailbox on Telecom's Yahoo/Xtra service but they use their own domain when sending messages, we are their MX host and we redirect their mail to their xtra.co.nz address. Apparently from the end of September Telecom are going to prevent their customers from using their SMTP servers unless the From address on outbound email is an Xtra one (or I presume a domain that they manage).
Their web site mentions that smtp.xtra.co.nz is going away, being replaced by send.xtra.co.nz http://www.telecom.co.nz/help/internet/smtpupdate.html It doesn't mention the other bit about the From line. I regularly change smtp servers as I move around networks.