SendMail exterior Exchange Internal

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http://www.linuxquestions.org – I am using sendmail in my DMZ and exchange 2007 for my internal mail server. This was configured before I started here and is not likely to change soon. The problem I inherited is this When a client goes to our web page and puts in contact info. 2 emails are sent. 1 internally to our sales dept. and 1 to the client with an attachment. The internal email is recieved fine. The external email always fails nomatter who it is, with error (#5.1.2 SMTP; 550 Host unknown> #SMTP#) It says the generating server is the sendmail server in the DMZ, not the exchange server, on the NDR report i recieve. T (HowTos)