We recently got ourselves in a bit of trouble with our email provider when we reintroduced some old email addresses to our account. A ton of them bounced, we got some SPAM complaints and someone was so angry that they contacted our provider personally to complain. We wound up removing said email addresses from the account in accordance with a request from our email provider.
The statistics in this infographic from Sample E-mails points directly to some of the issues that we hit head on. 30% of people change email addresses annually, 21% of people report email as SPAM even when they've opted into it, and 43% of email recipients report email as SPAM after reading the “from” name without even reading the email!
IMO, this dance between ISPs and ESPs is absolutely nuts. And personally, I don't think any of these actions have actually helped me to rid my inbox of SPAM. Quite the opposite, more and more valid emails are being put in my Junk folder – causing more and more communication breakdowns between me and the clients and prospects so important to me.