My e-mail server is getting a error response when sending mail to gmail accounts:
status=deferred (host gmail-smtp-in.l.google.com[18.104.22.168] said: 451 4.5.0 SMTP protocol violation, see RFC 2821 s12si416928qbs.9 (in reply to end of DATA command))
What is it, and why this problem is only with the gmail server?
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