PHP Mail Relay via Remote smtp Server

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http://serverfault.com – We have a php application running on Linux which sends emails to there users. Currently its setup like php.ini is configured to send via local sendmail server but we have separate mail server for our organization for this domain. I want to send the php application emails via that remote smtp server so these emails can have the correct SPF records and sign via DKIM. But I could not see such option in php.ini to specify the remote host address to forward emails to that, its for windows only. I saw some post which suggest phpMailer but I could not find how to configure that so all our php app (HowTos)