Email Subscription Help...

I have a bit of an odd question for anyone out there that might be able to help me. It's regarding my email subscribers. Lately, I've had a few people that have unsubscribed, which is fine, tastes change or they may even be subscribing using a different format.  But, the reason they gave was that their "ISP requested removal." I'm just a bit confused by that, it's not like I'm posting anything thing questionable or of adult nature.

Perhaps there's a setting on blogger that I have clecked by mistake and those ISP's think it's a bad site.  The only obvious setting that I know of is under Settings - Basic - Adult Content.  I've always had this marked as No.

Anyway, hopefully there's someone out there can can shed some light on my problem.  It also just occurred to me that this could be an issue with how I set up my email subscriptions.  Any suggestions?

Thanks for the help! :)