With many of today's email services like Yahoo mail and Hotmail, customers can configure their email account to more efficiently process their incoming mail. Typically, a person is able to create a list of "known senders", or a "friends list", and email that comes from the people on the list goes straight through to the inbox.
If you are sending mail to someone who has not put you on these "known" lists, your mail is still being delivered. The downside to not being on these safe lists, though, is that your mail is likely going into a bulk folder or will be subject to email filters. Although there is not much you can do about landing in the bulk folder at this time, there are some steps you can take to minimize it.
1. Place a reminder in every email you send asking the recipient to add you to their address book.
2. Place a note on your subscribe confirmation pages asking the subscriber to add you to their address book now to make sure they get the next issue.