Helen welcome to blocklisting, filters and other nasty things.
Are you using opt-in, or opt-out as i block out out companies on sight for opt-out and any firm that tries to sign me up to extra lists is filtered (zatz). so no email from them just a nice deny message
I dont block on bcc.
Remember there server there rules. Since somebody as deemed your mass mailing 'spam' can i send you all mine ?