I have a messaging system on my app where users can send messages directly to other users straight from my domain (not going through Mailchimp's Mandrill templates or Google Apps). I also have cron jobs that sends users' statistics to about 5,300 users every week. Again, the script sends messages straight from my domain.
Most e-mails are going to users' spam box, which I need to fix as soon as possible. I recently found out an app that tests e-mail deliverability and gives scores based on how well configured your email server is (among other things). This is the URL https://www.mail-tester.com. I was able to fix several things and my score went up from -0.2/10 to 7.7/10. However, although the tester says my e-mail is "good stuff", I know hundreds of emails are either not being delivered (returned because sender is not trusted) or going straight into the spam box.
The last thing I need to fix to have an almost perfect score is to add a DKIM signature to the emails. Hopefully that will increase deliverability rates. This is the message the email tester gives me about DKIM: "Your message is not signed with DKIM. DomainKeys Identified Mail (DKIM) is a method for associating a domain name to an email message, thereby allowing a person, role, or organization to claim some responsibility for the message."
I did try to work this issue out with my server (BlueHost) but they were not able to help me (they helped me with other issues though).
Additionally, I used Microsoft's mxtoolbox (http://mxtoolbox.com/) to test my email and the result of tests says a DMARC is missing or invalid.
Does anybody know how to add a DKIM signature and DMARC to emails that come from the domain itself. Are there a command lines that I can use to do that?
P.S. App is written in PHP