Gmail keeps marking emails coming from my site as spam. Is there any way to set up a filter that will send any emails coming from that domain to my inbox?
You can check for common issues with mxtoolbox http://www.mxtoolbox.com/? Try the blacklist and spf test first, and fix those if they are not defined.
You can try clicking 'Not Spam' button. Gmail may not send it to spam anymore.
Another way is to click 'Filter messages like this' under More Actions and click 'Next' in first step after making necessary entries if necessary. In the 2nd step, put a check mark on Never send it to Spam. You will also get an option to Also apply filter to ? conversations below. This will enable you to move other mails from same address out of spam.
Actually, you can create a filter with just the domain and tell Gmail to always mark as important. This'll mean that anything coming from that domain will not only be delivered to your inbox but be in your "Importnat" emails list.