We use a sophisticated emailing service, Mailchimp, based here in Atlanta, Georgia. They are kind enough to provide us with a discounted charity rate. It is a service with 3.5 million users who send out over 4 billion emails every month.
Needless to say, this service is highly automated. One of many things it does automatically is handle email bounces. If it sends you an email and that mail bounces back, then the way the system handles it will depend on the reason for the bounce, and/or the number of bounces. When it determines that mail is not getting through and is unlikely to get through, it will move that email to an inactive list, so as to avoid needless waste of bandwidth (they are mailing 4 billion emails a month, so inactive email addresses can be a big issue).
If you unexpectedly stop receiving our emails, it could be due to one of a number of reasons. It might simply be that the spam filter used by your email provider (and most use one behind the scenes) mistakenly flagged our email as spam and it got bounced back.