I quite often work away from home, using other people's WiFi (legally) to access the Internet and my email. I use Thunderbird as my email client for my 4 separate accounts. Since I am a BT Broadband customer, I use their smtp server as my outgoing server. Not so long ago, all such "foreign" email accounts had to be confirmed with BTBB - which I duly did. Now I occasionally get "refused access" when sending emails with attachments.
Some time ago, I heard that there is a (paid for) smtp server service for users to send through - anyone heard/know of it?