getting mail into your inbox

After building a CRM system for a company, we noticed that all of our marketing emails were hitting the Gmail's Spam folder.  A little Trial and Error revealed some interesting facts about how Google's Spam Filter works.

The problem we were having was our Server based CRM system that allows our Account Manager to quickly market our products to potential customers, was getting filtered by google.  All Messages were going directly to the spam folder.  However when the Account Manager copy pasted the same message into Thunderbird and manually sent it, the message went to Gmail's Inbox.  This ruled out the possibility of the IP Address being an issue since both systems would send email from the same IP.  This lead me to believe that either the messages were being formatted differently, or Gmail was reading the Delivery Headers and accepting messages that originated from a Residential Comcast IP, rather than messages that originated directly off the mail server ( Web Mail, or Server ).

Both messages looked exactly the same.  Both had 4 hyperlinks back to our website, same text, ect.  However at the bottom of our messages I setup a signature that included the company logo.  Turns out that when this logo is being referenced from the web server <img src="http://mywebsite.com/mylogo.jpg"> Gmail would always push the message to the Spam Folder.  However when the logo was embedded into the email <img src="cid:mylogo">  with a base64 block storing the actual image data, the email would make it into the Inbox.   I guess for security and privacy reasons, Google feels you should be penalized for Server Referenced images in your emails. 

So in the future if your emails keep hitting the Gmail Spam folder, try to embed your images into the email rather than reference them from your web server.