- Plesk for Windows
- Mails cannot pass DKIM validation in Gmail mailserver:
CONFIG_TEXT: dkim=neutral (bad format) email@example.com
- SmarterMail is installed and its version is below 16.3.6600 (Tools & Settings > Server Components > Mail Server > SmarterMail).
SmarterMail issue, which was fixed in version 16.3.6600 (Jan 26, 2018) refer to SmarterMail forum thread for more details.
Consider updating SmarterMail to version 16.3.6600 or higher.