[IMail Forum] Undeliverable mail

[Matt Warren]

Hi, when I try to send an email to a user from an outside company I get:   Unknown user: [EMAIL PROTECTED]   RCPT TO generated following response: 550 5.7.1 Unable to relay for [EMAIL PROTECTED]     This is weird because I have been able to send him mail regularly in the past.  I tried it twice and got this message.  I am sending from inside the company network by the way.   thanks     Matt Warren IT Technician A+ N+ MCP MCSA 414-847-1207 Ken Cook Co.