Remote Server returned '550 5.7.520 Message blocked because it contains content identified as spam. AS(4810)'

I encountered one of those bounce messages yesterday (not the exact same but a variant). I usually get this a few times a year and it will reference my email providers IP address. I would normally contact my email provider and they handle it.

I have not done anything about the current bounce as yet but will give it some attention later today as this so far is a one off.

Who is your mail provider and what DOMAIN were you sending to?