ISome subscribers with a Gmail-address
does that mean, that not all subscribers with gmail address don't receive the newsletter?
By the way, for me the problem seems to be, that Gmail rejects the newsletter. One reason could be, that the sender is blacklisted, either by IP, by domain or by email address. Another reason could be, that Gmail blocks a sender, if it sends more than x mails per a time frame, like T-Online does. At T-Online one have to contact T-Online and ask them not to block this sender, because this is a wanted newsletter. Mostly they will agree.