I cannot send email while connected to Vodafone, 3, Orange, O2 or another ISP.

Some ISPs will only allow you to send email through their email server. You can circumvent this restriction by going into the Advanced or More Settings for the SMTP server in your email account settings and changing the port number from 25 (the default) to 587. You can leave it set on this and use port 587 on any network and in the office.

You can view this article online at:
http://www.domaindevils.com/support/knowledge_base/index.php/article/cannot_send_email