Accessing Plusnet mail from a mobile phone

[#1]

I've been trying to set up an Android phone to check a Plusnet mail mailbox. I thought I was going mad when it would send mails inside the house, but not when I was away. Then I realized that inside the house it's using my Wifi, and elsewhere it's connecting via T-Mobile. So I was thinking that Plusnet's SMTP server won't do the business from elsewhere.
Can this be it? And if so, can anyone suggest alternative settings on the phone from the standard Plusnet mail account setup to get it working?
On the main PC I've been using POP/SMTP so I can do fancy filing in Outlook, and would use POP/SMTP on the phone too (but without deleting on the POP server on access from the phone, so that it'll all come to the PC when I get home.) I'm a bit nervous of IMAP synchronization.

[#2]

You can use PN's SMTP server (unless T-Mobile block access to any but their own) but you need to tell your phone to use authenticated SMTP and enter your account user name and password (the same details as for accessing the PN member centre).
If T-Mobile block access to other SMTP servers then replace the PN server details (relay.plus.net) with theirs (smtp.t-email.co.uk).  Leave the incoming settings set to PN's POP or IMAP server.