Today I ran into a very strange problem. I’m running an Exchange Server 2010 SP1 and an Exchange Server 2007. The Exchange Server 2007 is inside our company’s network, protected by a SecurePoint Firewall. The SecurePoint Firewall is having Greylisting enabled, so sendmail is filtering all the mails flowing to the E2K7. Whenever I sent an email from the 2010 SP1 (outside the firewall) to the Exchange Server 2007 (behind the firewall), it was returned with the error message
554 5.7.1 Command rejected after the SMTP "DATA" command was sent.
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