There are many different spam filters with their own methods and rule sets, so there is no easy way to get all your mail into the inboxes of the recipients.

However, there are a few simple rules that reduce the probability of spam classification with little effort.

1. Send only with the consent of the recipient

2. Always provide a clearly visible unsubscribe link

3. Always add a complete imprint in plain text

4. Avoid using a generic or shared sending domain

5. Use as few different domains as possible within headers & content

6. Never use deceptive subject lines, From names, reply-to addresses or content

7. Ensure a reasonably balanced text to image ratio and avoid large invisible text parts.

8. Always add a text version

9. Never use URL labels that might look like phishing (e.g. Label contains a different URL than the URL itself)

10. Never use email addresses as From or To aliases