Sender domain must exist (in reply to MAIL FROM command)

HCL Domino Domino Forum
1

I am getting this error when trying to send an outside email. Sender domain must exist (in reply to MAIL From command) Does anyone have an idea what this might be?

Thanks

BM

2

Subject: Sender domain must exist (in reply to MAIL FROM command)

It means the @domain.com cannot be resolved in DNS by the server so it rejects the mail as a possible spoofed domain.

The domain.com should resolve via DNS MX records to a legitimate mail host.