Authenticated SMTP - but only if you use Plusnet email address?

[#1]

Just switched my broadband from BT to Plusnet - all went smoothly apart from getting my email working properly.
I work from home and my incoming email comes from my work email account/hosting provider and this still works fine as I've not changed any settings. When I had BT Broadband all my devices (laptop, phone, ipad) were setup the same, all sending email via BT's authenticated SMTP. So no matter what network I was using, be it home WiFi, coffee shop or hotel WiFi, or 3G on my mobile, I could send email without any problems.
Now I'm on Plusnet broadband, I can send when I'm on my home WiFi, but the authenticated SMTP simply won't work on any network (including home WiFi).
Am I right in thinking that Plusnet authenticated SMTP only works if you receive AND send email, via a Plusnet supplied email address?

[#2]

Are you using the correct username and password? These are the username and password that you use to log on the default email account using Webmail https://webmail.plus.net/

[#3]

Hi itsme, thanks for responding. I've tried all the login details I have been sent by Plusnet and can't gain access to the Webmail.
dick:quote

[#4]

Hi itsme.
Thanks for pointing me in the right direction. I setup a plusnet webmail account, which I'll never use, but this allows me to use Authenticated SMTP in exactly the way I want to