Spurious outgoing spam blocking

[#1]

I'm trying to send a perfectly innocuous message to friends. It was rejected when I sent via a mail client, so I tried using the Web interface, and it was rejected again. I've no idea what the problem is (and I have a reasonable grasp of the principles of spam checking).

How do I get my message sent? I've tried some rewrites. I just keep getting 552s. Other messages have gone fine.

[#2]

Hi @dplusr, sorry to hear you're having problems sending an email.

I've raised a ticket on your account regarding this Here, so we can look in to this further. If you could respond via the ticket with the requested information, I'll get back to you as soon as possible once I've had a chance to look in to this for you.

Thanks.