Cablevision - Optonline - Outbound Mail Filtering?

Cablevision's customer support for Optonline says that they do not do outbound mail filtering. They certainly do inbound mail filtering to catch spam.

However, for the last week or so, my email from my Optonline address has not been delivered. So this morning I started experimenting between my (web-based) yahoo, gmail accounts and my optonline account both from my laptop and from Optonline's web-email interface.

I discovered that

1. Email, when delivered between the three services, is virtually instantaneous.
2. All outbound email from Optonline, whether from my laptop or from the web-email account, that contains my blog URL: http://arunsmusings.blogspot.com is not delivered (or, more accurately, as of writing has not been delivered).
3. All outbound email from Optonline, whether from my laptop or from the web-email account, that does NOT contain my blog URL, has been delivered.
4. Optonline does not deliver inbound email from Yahoo and Gmail if it contains my blog URL.
5. Optonline does deliver inbound email form Yahoo and Gmail if it does NOT contain my blog URL.
6. Between Yahoo and Gmail, all mail is delivered, both with and without my blog URL.

My email signature commonly has my blog URL.

Seems clear as fine camera lens glass to me that Optonline does outbound mail filtering, even though their service desk denies it.

Using their webmail demonstrates that software on my PC cannot be responsible.

The three questions are:

1. Why?

2. How did my blog URL get on their list? I do not send out email to anyone who is spiteful enough to put my blog URL on a spam list. BTW, I tested using another blogspot URL, and those emails were not blocked.

3. How does one even submit a URL or other text string to be blocked? I don't see how going through the optonline pages. However this is happening, I think a hacker has to be involved.

Slashdot has a thread from 2008 on outbound mail filtering. Cox Cable also does it, and a blocked URL is mentioned there.

I tried to send an email. The email only contained text. The text Cox objected to was "http://my_homebox_IP_number/"

PS: My best guess is that someone has put my URL on a internet gambling or child pornography list - those are the only reasons I can think of for blocking a URL in email.