First of all, I want to thank you for your time. I\'m having a hard time getting my head around this problem.
With reference to this thread we\'ve dediced to implem
Spam issue because of following reasons
1)Shared hosting
If you are using shared hosting, PHP is not the solutions for this issue.try to contact your server providers.Some time your hosted IP treated as spam.Try to change the hosting providers, It may work fine.
2) More Links in your e-mail body
3 )Partial header(Always use reply-to,Ref Ans:TrentonMcManus)
4) Bulk E-Mailing
5) Spam Reporting(number of people who have clicked on your link as spam)
6) The message not to be too short or too long.
7) Sending From Blacklisted IP(hosting, and SMTP server) )
It may be new your IP address has been previously blacklisted by Google or Hotmail You can check Blacklisted ip or not from the site from here
8)Verifying sender IP
Sender Policy Framework (SPF) is an email validation system designed to prevent email spam by detecting email spoofing, a common vulnerability, by verifying sender IP addresses.
Perhaps PHP not solutions for this. You can do Following things in php coding
1)Always use the from/reply to address
2)Add unsubscribe link in body
3)Avoid spam keywords.
4)The message not to be too short or too long.
5)Text version is better than HTML