Where many email clients send messages that appear to be from spammers or contain spam or are from any sender who’s not in the recipient’s address book or contact list. Some clients allow the recipient to override the system’s settings and direct that mail from a suspect sender be sent directly to the inbox. E.g., Yahoo!Mail gives recipients a button marked “Not Spam” on every message in the bulk folder.

The 3 Things To Avoid When Emailing Your List
When you decide to have an opt-in list, it is not just a matter of sending your subscribers your promotional newsletters or catalogs.