Don't get yourself onto spam block lists, which can relatively easy happen if your mail server is misconfigured. You can test the spam-level of your outgoing mail on this site: https://www.mail-tester.com
you send a mail to the displayed address and it will parse the incoming mail and analyzes the message headers. the headers contain valuable information about the authenticity of the mail. If a mail looks authentic to the spam filter, it will be marked with a lower spam score.