We all don't like spam, but sometimes, there are good reasons to send large amounts of automatically created e-mails. Order confirmations, newsletters or similar services. Sadly, I often see how it is done wrong, and would like to propose some rules how to send mass e-mails correctly. 

The risks of doing it incorrectly are two fold: Your e-mail will get caught in spam filters, or your e-mail will teach users to fall for phishing, endangering your brand.

So here are some of the rules:

- Always use an address as "From" address that is within your domain. Even if you use a third party to send the e-mail. They can still use your domain if you set them up correctly. If necessary, use a subdomain ("mail.example.com" vs "example.com").
- Use DKIM and or SPF to label the e-mail as coming from a source authorized to send e-mail on your behalf. DKIM can be a bit challenging if a third party is involved, but SPF should be doable.  Using a subdomain as From address can make it easier to configure this. For extra credit, use full DMARC to setup e-mail addresses to receive reports about delivery issues.
- Use URLs only if you have to, and if you do, don't "obscure" them by making them look like they link to a different location then they actually do. Use links to your primary domain (subdomain as a work around).
- Try to keep them "plain text", but if you have to use HTML markup, make sure it matches the look and feel of your primary site well. You don't want the fake e-mail to look better then your real e-mail.
- watch for bounces, and process them to either remove dead e-mail addresses or find our about configuration issues or spam blocklisting quickly.

Of course, I would like to see more digitally signed e-mail, but I think nobody really cares about that. 

Any other ideas?

------
Johannes B. Ullrich, Ph.D.
SANS Technology Institute
Twitter