Postfix Relay to Office365

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http://serverfault.com – I am trying to setup a Postfix server on a Linux box to relay all mail to our Office365 (Exchange, hosted by Microsoft) mail server, but, I keep getting an error regarding the sending address: BB338140DC1: to= relay=pod51010.outlook.com[]:587, delay=7.6, delays=0.01/0/2.5/5.1, dsn=5.7.1, status=bounced (host pod51010.outlook.com[] said: 550 5.7.1 Client does not have permissions to send as this sender (in reply to end of DATA command)) Office 365 requires that the sending address in the MAIL FROM and From: header be the same as the address used to authenticate. I (HowTos)