Jeff Crosby wrote:
her network people say it's because our site is listed somewhere as sending spam.
How do we find out if we're listed anywhere?
http://openrbl.org/query?188.8.131.52 It doesn't look like you are blocked anywhere from there, but SpamCop shows you listed on dnsbl.sorbs.net http://www.dnsbl.sorbs.net/ Also, any mail server administrator could have you blocked on their system. Some might have blocked all rdns of verizon.net or bdsl.verizon.net or by IP range, etc. You could try sending a request to their postmaster@ account asking for clarification or just give them a call.