okay, maybe I can explain better. All authorized mail is DKIM signed. This means that webmail, smtp, etc, mail that users must sign in for is signed, both domainkeys and DKIM.
Mail sent through scripts, as php, using sendmail ARE NOT signed, because it is easy to forge any aspect of the mail. This is why your mail possibly goes to spam.
Solution, pipe your mail through smtp. Most CMS scripts support this.
Next, Google sends unknown IP addresses to spam, not always, but if your mail matches any filters, it will go to spam, until enough Gmail users mark it as 'not spam'. I have asked Google the amount, and have never been answered. However, my main IP for my hosting company has finally started to go to inbox. Having the email properly signed, spf records, etc, makes this process faster. Or, as I have just found out, my latest server sends directly to inbox. Why? Ask Google... it is identical to the other 5 servers.
Send them email, explain your position, your company... etc. Be sure you meet all the requirements, opt-out links, etc. It all matters.
