Hi, I've been sending emails to a small group of colleagues for a while via Thunderbird. I enter my own email address in the 'To' field, and their email address in the 'BCC' field, as I would prefer for the recipients to not know who else is included in my list. Nothing malicious, just I'm offering work to my list of freelance staff.

In the past it's been fine, but recently, the emails have stopped sending, and I get the following error message:

An error occurred while sending mail. The mail server responded: 4.7.1 Error: too many recipients from 193.152.181.129. Please check the message recipient "ken@westcoast-mountainguides.co.uk" and try again.

The email address in the final line of the error message changes, but ultimately, I cannot send the email via Thunderbird, and have to resort to saving it as a draft, and then sending it via Webmail instead.