Sending email via Plusnet SMTP server abroad

[#1]

Hi, I use the Plusnet SMTP server (relay.plus.net) to send out personal emails on my mobile devices (eg, iPhone, iPad).
I use password authentication on port 25. My email is of the form someone@plusnet_hosted_domain.co.uk
This works fine in the UK when my device is on a 3G network or a wifi network. However, it fails when I am overseas. Is this blocked as an anti-spam measure? Is there an alternative solution?
Any advice would be most appreciated.
Derek

[#2]

Some networks block access to port 25, other than to their own servers. I use authenticated smtp when in Portugal both on Wifi and on the Vodafone 3g  network so its not a general overseas problem. 

[#3]

Hi MrW,
Interesting. Of the overseas wifi networks, one includes a domestic network hooked up to the French ISP wanadoo.fr. I could send out emails via a SSL-protected Exchange server but not through relay.plus.net on port 25.

[#4]

Yep, Orange/Wanadoo are definitely one who block port 25. You should be able to send via their server though. Its just a matter of finding what it is and then ( temporarily ) changing your outgoing server details. If you use Thunderbird for example you can setup multiple outgoing servers and select which one to use when sending.