Summary

Propertybase Support/Development can do very little about why an email is going to SPAM but can recommend the below procedures to reduce emails going directly to SPAM.

Guidelines

Things to look out for:

Certain actions can cause an email to be redirected to SPAM automatically by the email client. This includes but is not limited to the following words used in the email:

• Alert
• Notification
• Approved
• Dollar Signs
• ALL CAPS AS EMAIL TITLE
• Another client hits SPAM all email could be redirected to SPAM
• Non-Whitelist IP Address/es
• If too many emails have been marked as SPAM, the email address could be BLACKLISTED (An email address can also be Blacklisted if you break any of the CAN-SPAM laws.)
• Broken links
• Missing alt descriptions of images
• Other oddities in the email source code
• Lastly, if our customer's recipients are flagging the email as SPAM, eventually, their email address could be blacklisted, which is NOT something WE SUPPORT.

Things to consider: 

• Font Size 
• Email Signature 
• Is it a real email address and coming from a specific person?

We are very hesitant to debug custom email templates for our customers as there are so many variables that could cause an email to go to SPAM. 

There are also some other great articles and literature available online that give users tips and tricks on how to avoid being directed to SPAM. (There are even applications that help manage there over SPAM score.)

Definitions/Context

Blacklist Definition - An email Blacklist is a real-time database that uses criteria to determine if an IP is sending an email it considers to be SPAM. There are several blacklists… Each list [has] a unique way of accepting inbound mail and determining if the email is considered SPAM. This can all impact deliverability for users/customers' emails.

FAQ

Q: How can I tell if my email has been Blacklisted?

A: To see if an email has been blacklist, please check this site.