Email within organisation using private server

Hi, I am trying to send email within organisation using private wired LAN. I have tried with Ethernet shield and Arduino Mega, but couldn't succeeded. Serial monitor shows that mail sent successfully but server consider it in junk mail box. I tried with Phpoc shield also. But Phpoc shows that mail failed.

Can any one help me to send email within organisation using private server (not Gmail)

Easy. Change the junk settings on your server.

Email servers on a private LAN would not normally be configured to accept incoming mail from random addresses.

Speak to the people who run your mail server.