User noamoss encountered an issue with emails not being sent in their Discourse installation (1.7.0 Beta 2 + 8), resulting in a “501 Syntax error” in the mail logs. Despite checking the host name, services, and locale settings, the issue persisted. However, after reinstalling and reconfiguring, the problem disappeared. noamoss suspects that the issue might have been caused by an Hebrew email site title entered in the admin/site_settings/category/email, which could be a consideration for future instances of the “501 Syntax error”.
The problem disappeared after reinstalling. After reconfiguring my guess is that I might have entered an Hebrew email site title in the admin/site_settings/category/email.
Should consider it when you see “[Sender] 501 Syntax error” in the future.