Mail Server Setup
MTA-STS and TLS-RPT: A Practical Setup and Troubleshooting Guide
Understand MTA-STS policies and TLS reporting, check the required records and plan a careful rollout before enforcing transport security.
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The MXValidation blog
Mail Server Setup
Guides to configuring and maintaining your mail server, covering Postfix, Exim, reverse DNS, EHLO and TLS. Check the settings that affect how receiving servers identify and accept your email.