Email Marketing Best Practices

• ESPC
  (PDF) Email Senders and Providers Coalition's best practices guide. The ESPC is a cooperative group of industry leaders working to create solutions to the continued proliferation of spam and the emerging problem of deliverability.
• FTC CAN-SPAM Law
  The CAN-SPAM Act of 2003 (Controlling the Assault of Non-Solicited Pornography and Marketing Act) establishes requirements for those who send commercial email, spells out penalties for spammers and companies whose products are advertised in spam if they violate the law, and gives consumers the right to ask emailers to stop spamming them.
• Guidelines for Proper Mailing List Management
  
• MAAWG: Sender Best Communications Practices
  The purpose of MAAWG (Messaging Anti-Abuse Working Group) is to bring the messaging industry together to work collaboratively and successfully address forms of messaging abuse such as messaging spam, virus attacks, denial-of-service attacks, and other forms of abuse. MAAWG offers guidelines for high-volume senders.
• Minimize Email Complaints
  (PDF) A nice guide from Truste that provides some guidelines on minimizing spam complaints.
• SpamCop.net
  Read this if you want to reduce the number of spam complaints you receive.

Email Marketing Analysts and Research

• eMarketer
• Nielsen Norman Group
• Jupiter Research