Let first start by saying it is NOT 100%, nor will it EVER be 100%! If any service has told you their delivery rate is 100%, then run, don’t walk, but RUN away!
Many AutoResponder services report the deliverability rate based on the amount of bounced messages they receive. So, if they send 100 messages, and 2 bounce back, they report their deliverability rate to be 98% What they DON’T tell you, is that just because a message did not bounce, does NOT mean it has been delivered! Many ISP’s use all kinds of criteria to drop messages without it ever even getting to the user’s Inbox or Spam box. They just drop the message!
We have employed a company specializing in reporting delivery rates. They setup hundreds of mailboxes at all the major ISP’s around the world. Those email address get’s added to a special list on our side. Whenever we send a message to that list, then the company goes and checks every Inbox, and every Spam box on all those ISP’s and gives us a REAL deliverability rate report.
We have also setup ALL the requirements set forth by the major ISP’s. (This gets a bit technical) We are fully compliant with SPF, DomainKeys and DKIM. We have a fully functional FBL (Feed Back Loop) setup which is running automatically in the background, and this FBL has been registered with all the major ISP’s which use a FBL service.