Comcast Blocking Again!!

[#1]

I've had messages bouncing this morning from Comcast again.

Quote

The following message to <xxxx@comcast.net> was undeliverable. The reason for the problem: 5.4.7 - Delivery expired (message too old) 554-'IMTA18.westchester.pa.mail.comcast.net comcast 212.159.7.35 Comcast block for spam.  Please see http://help.comcast.net/content/faq/BL000000 '

Can someone please explain why we have constant problems with Comcast?

[#2]

Being one of the larger US ISPs means they are a prime target for spam - and therefore have the most aggressive spam 'solutions'.
B.

[#3]

Barry, thanks for your comments.  Am I right in saying that if PN is being blocked by Comcast then specifically PN must have been used for spam.  If that is the case I ask why PN can't stop the spam from being sent in the first place. Isn't IronPort supposed to do this?

[#4]

I don't think IronPort is being used for outgoing email - yet!

[#5]

I am sick and tired of Comcast, I can never get through to my friends in America. Another message returned today. Looks like I'll have to set up another account with a different ISP to be able to contact them as they are constantly blocking PlusNet.

[#6]

Same here, I'm always getting my emails returned.  Can someone from PN please explain why this problem keeps happening?

[#7]

Just received 2 more bouncing messages from Comcast.  Any news on this?