I own a catering business and we rely on quotes coming from our website. I recently found that some customers never saw our replies because they were flagged as SPAM. Normally the process is for someone to send a response via Contact Form 7 within WP. We then reply to that email. I thought that had something to do with it (the customer's original email didn't originate at their ISP).

However, we recently sent a customer an email that didn't originate with the website and it went to the customer's SPAM box (RoadRunner ISP). We simply drafted up and sent the email from RoundCube. I've looked at the email and don't see anything questionable. There are no links, no attachments. We did CC a different email address on our domain, but that doesn't seem a logical reason to flag it.

I checked our domain name on http://mxtoolbox.com/ and don't see it listed on any blacklists. I do see it on a BACKSCATTERER list. Can that cause my email to go to SPAM? Any thoughts?