Having put some time and effort into getting my mail server setup, and configuring my Android phone to use IMAPS for receiving and SMTP over TLS for sending emails, and testing it, I was quite annoyed while out in the town to find that I could receive mails but not send any.
It turns out that 3 Ireland, when on the 3ireland.ie APN block all outgoing connections on TCP port 25 e.g. the SMTP port. They do have a mail relay that is permitted available, though documentation for that is hard to find. The mail relay is located at:
mail-relay.3ireland.ie
However, using their relay would defeat the purpose of having the secure SMTP service available. Simple workaround is to change the port forwarding on the router to direct TCP port 587 externally to port 25 internally – no config changes on the server required.
