mambo: email goes to spam

I built a site on mambo v 4.5.2 and

under Global Configuration tab -> Mail set PHP mail function option

but if I send email from abc@hotmail.com it goes in to SPAM

however if I u开发者_开发知识库se abc@gmail.com it goes in to Inbox. There is a screen shot.

There are lots of reasons; there is a good summary up by the SO authors.