I've work all day long on that crazy problem.
I created an HTML email that will be sent massively. I Use PHPMailer and I tried Mail Function. Both PHPMailer, it's SMTP feature and the native Mail Function works well.
GOOD - PASS THE SPAM FILTER
The problem is when I put a link in the HTML code, the email turns into SPAM. But not any links. If I put a link that the href is "http://www.google.com" then It passes the filter. Samething on my company domain name "http://www.sequencedigitale.com", it passes the filter as well.
<a href="http://www.google.com">This is Google Website</a>
WRONG - DON'T PASS THE SPAM FILTER
What turns me crazy is when I put the same domain name as the server that process the email submission. I have 3 domains names that point on that server, every of those 3 don't pass the filter.
<a href="http://careers.fieracapital.com">This doesn't pass the filter</a>
I checked on some Blacklist checkers and the IP isn't block on 100% of the lists.
The IP is 184.107.100.61
The problem happened to me on Hotmail, Outlook and on a Server runned with Plesk. It passes the filter on GMail.
Any help will be appreciated.
Thanks.
Carl.