Unable to send email when away from home

[#1]

I thought I had this sorted so that I could send mail when away from my plusnet connection. Mostly it works, but sometimes it doesn't. Why? I'm using the setting I was advised to when I first encountered the problem. Outlook 2016 on Mac.

I'm not aware of any friends who have similar problems with different ISP and given plusnet is effectively using BT kit why is it such a problem? 

Iain

[#2]

From https://www.plus.net/help/email-guides/how-to-set-up-plusnet-email/

You'll need to give a few more details when you're setting up your email application. They can be pretty confusing, so here's what to use.

	IMAP	POP
Incoming server	imap.plus.net	mail.plus.net
Incoming port	143	110
Outgoing server	relay.plus.net	relay.plus.net
Outgoing port	587 (recommended) or 25	587 (recommended) or 25
SSL/TLS	No	No
SMTP Authentication (only needed if you're sending emails from a non-Plusnet Internet connection)*	Yes	Yes

* This is only available if you've got an active Plusnet broadband account

If you've been with us a while, your domain might be '.force9.co.uk or '.free-

So try port 587 on the outgoing server

[#3]

I'll try that next time. Still don't understand why plusnet have this bug!