Using 3g dongals can sometimes block outgoing mail settings even on authenticated email sending.

This is down to smtp port 25 being blocked

Solution:

Got into your account settings and change port to 587 and click send and receive things should work.

Related posts:

1. Mobile Me SMTP Settings
2. Irish SMTP Outgoing Mail servers Vodafone, Eircom, 3, O2, Gmail, Magnet
3. Access your computer from anywhere
4. Virtual memory low
5. Freshbooks Overdue invoice