Thank you for the clarification. The fact that John from the UK was able to connect to Rogers' SMTP service presumably means that his ISP is not blocking port 25 connections from "foreign" sources. This is, perhaps, surprising these days.
Indeed - I'm with Zen Internet, and they do not block or otherwise interfere with anything. I have a /29 IP block which is fully configurable from my ISP dashboard, so I can create DNS records for my IP range without having to bother anyone at Zen.