Will ISPs accept mail from a postfix null client with no dns record

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http://serverfault.com – I am concerned my mail server setup may cause some ISPs to reject mail that is sent by it. I am using Postfix to send mail for a web application, light load, user notices. It also sends cron notices and "monit" alerts. It is for sending mail only. I guess it wants to be "null client". The postfix server and webapp live on the same box. The webapp builds the "to" and "from" email mail headers. Server: 123.foobar.com Website Domain: mysupersite.com Mail that is getting sent by postfix has: from: [email protected] HELO: 123.foobar.com ( (I am not sure this is enough header (HowTos)