dstiles - 7:18 pm on May 17, 2013 (gmt 0)
Don't seem to have any records for that ISP, which implies no problem.
Bill - I've seen several DNS lookups for DSL which have "host" in the response. I would not block on that alone. It would be useful if a suitable TXT comment was included in DNS records: an increasing number do but so many do not.
I also look very suspiciously at IP ranges with the email address as hotmail, gmail and similar.