Getting email to the Inbox isn't easy. Return Path estimates that twenty percent (20%) of legitimate email is not delivered to an inbox. Legitimate senders of bulk mail must monitor and enforce delivery settings for each email recipient domain based on published, or sometimes unpublished, policies. This is very crucial when delivering to larger email providers such as AOL, MSN, Yahoo, etc. Each email provider has its own policies regarding the exact settings they require from each sender of bulk mail. Sending too many email messages to YAHOO in one connection might damage your reputation & brand.