Reasons for VPS mails to be received as spam on remote hostsEvery ISP has custom anti-spam filters which recognize SPAM by:
1. The originating domain name - your domain might be associated with sending spam after customer complaints.
2. The server's IP address being blacklisted. You can check whether your IP is blacklisted using this online tool:
http://www.dnsstuff.com/
3. Custom anti-spam rules which look for certain words in the body / header of the email. For example 'Viagra', 'Free promotion' and similar.
4. Others custom antispam rules which are specific to the ISP.
SiteGround can assist you in point 2. If the server's IP is blacklisted for no reason, we can request the whitelisting. However, we can hardly assist you with the rest of the points and it is always recommended to contact the remote ISP and ask for further assistance.
