PlusNet & T-mobile issue

Surfer

I asked this question elsewhere. I use Plusnet broadband on my laptop at home for connecting and when out & about I use a T-mobile datacard Web 'n Walk on the same laptop. My issue is that I can receive emails but I cannot send them when using the T-mobile datacard.
I assume this is because the email account has Plusnet as the outgoing email server. I created a second account using the outgoing server "smtp.t-email.co.uk" but still no joy. The incomong server is still Plusnet. Can any one advise as the T-mobile website does not cater for people who use two different providers. Thanks.