How to make the mail via WordPress wp_mail not sent to the junk e-mail?

How to let the Wp_mail through the WordPress send mail not sent to the spam mail??
Company intranet based on Word press, will be in the corresponding time with Wp_mail to send mail to the intranet people, the problem is that everyone in Outlook received these messages are in the junk e-mail,
Ask how to let Mail can send to inbox inside!

(By the way, how does the email client identify the spam message?? ）

------Solution--------------------
What is junk e-mail

IT. Sohu.com 2004-01-01 21:04 turn from: Xinhua
Page function "I say two words" "I want to" pull "wrong" "Recommended" "Font: Big Small" "print" "Close"


Xinhua Beijing, September 18, China and some other countries in the world have their own definition of "junk mail".

In August 2000, China Telecom developed a spam-handling approach and defined spam as an e-mail advertisement, publication, or other material sent to unsolicited users, and no clear letter of return, sender, reply-to address, etc. Using the network of China Telecom to conduct violations of other ISPs ' security policies or terms of service, and other mail that is expected to cause complaints
Thing

May 20, 2002, China's education and research computer networks published the "Regulations on the suppression of Spam," which defines spam as: In general, without the user's request to forcibly sent to the user's mailbox any ads, promotional materials, viruses and other content of e-mail, generally with the characteristics of bulk delivery.

The Chinese Internet Association defines spam in the anti-spam code of the China Internet Association: Spam in this specification, including e-mails of the following attributes: (a) the recipient has not previously requested or agreed to receive advertising, electronic publications, various forms of publicity and other promotional e-mails ; (ii) e-mail that the recipient cannot refuse; (c) An e-mail message that hides information such as the identity, address, title, etc. of the sender, and (iv) e-mail messages containing false sources of information, senders, routes, etc.
------Solution--------------------
Messages sent using the Mail function will be considered spam. Instead of sending it with Phpmailer, there is no problem. How Word Press changed to Phpmailer I don't know, settings, plugins, modifications.
------Solution--------------------
http://www.baidu.com/s?wd=wordpress+phpmailer&rsv_bp=0&rsv_spt=3&inputT=6045

http://blog.csdn.net/ggggqqqqihc/article/details/2335536

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