Hi there - Looks like I have the same issue. Just signed up with Toob 900mbps and starting seeing issues with sending emails (receiving was fine). Spent a day pulling my hair out trying to figure it. My email client (Thunderbird) was reporting an issue with SMTP server... Spoke to Toob and BT and didn't really get very far. Then decided to use my phone as a hotspot instead of the Toob router and bingo can send emails again. So can anybody enlighten me as to what the issue is and how to recify ?
If you are no longer a BT Broadband customer your BTMail email account will be downgraded to a BTMail Basic account which can only be used on webmail and not with email clients/apps.
If it works with a hotspot but not via Toob, it would suggest your IP address allocated by Toob is on a blacklist.