1. Segregate the IP addresses you use according to what you use them for. Yahoo! Mail keeps reputation data about each IP address you send from. Consumer reports of spam negatively impact an address’s reputation data. Separating an address that delivers marketing mail from another that sends transactional mail (order receipts or billing notices, etc.) – or from another address that sends mail composed by end users – you make it easier for Yahoo! Mail to determine the IP address' reputation. This way a delivery decision can be made that will have the best chances of pleasing both you and (more importantly, in this case) your recipients.
2. Manage your lists by paying attention to bounces and rejections. Clean lists get higher-priority delivery than others.
3. Don't act like a phisher.
* Link to domains, not IP addresses. The Yahoo! Mail client warns users that IP address links are dangerous.
* Use standard ports. The Yahoo! Mail client warns users that links containing ports are dangerous.
* Don't include html forms in emails. The Yahoo! Mail client warns users that submitting forms in email can be dangerous.
* Don't include embedded objects in emails (like flash or active-x). The objects are stripped and will not run.
4. Use a consistent From: header address. Your domain name is an important element of your brand. Using it consistently helps us to distinguish your email from spam. Additionally, this not only helps users find your mail, it enables their filters to ensure your messages arrive in their inbox.
5. Be CAN-SPAM compliant.
6. Use email authentication such as DomainKeys. This will help us show users that the email is legitimately from you, and, if you sign all your email, it will help us point out the forgeries to users too. It will also help us to minimize delivery disruptions when you need to change or add IP addresses.
7. Pay attention to your reverse DNS of your IPs that send mail. If the reverse DNS entry looks like a dynamically assigned IP address instead of a static mail server, Yahoo! is more likely to downgrade your sending reputation.
8. Don't retry rejected messages. If we reject a message, we will not accept it anytime soon. Retrying the message wastes both our resources and makes you appear to have a dirty list.
9. DO retry 4xx messages. If we send a 4xx error, we will accept your message later -- keep trying a few times.
10. Secure your mail servers. Ensure your mail servers are not open proxies or relays. Keep your software up to date with the latest security patches to help prevent spammers from using your resources and tarnishing your reputation.
11. Secure your web servers. If you use formmail scripts, ensure they can not be improperly manipulated.
12. Use common-sense settings. While we have not published guidelines for numbers of connections you can concurrently use, we ask that you treat our resources with respect. The more you take, the fewer there are for others, which may force us to deprioritize your connections.
13. Don't use callback or challenge response systems for unauthenticated email. Yahoo! may be the spammers' favorite domain to forge. Emails sent to forged addresses likely will appear to be a dictionary attack to us and will be deprioritized.
14. When sending a bounce message, use the null address "<>" as the bounce address.
15. Don't use a null address "<>" when you are not sending a bounce message.
16. Test your email's look and feel with image placeholders. Many users won't see images in your email.