Have you ever wanted to be able to process the spam score of any incoming or outgoing email messages but didn’t want the hassle of managing SpamAssassin? Now you can use the lightweight JSON API on the spamcheck.postmarkapp.com website and instantly integrate spam score processing in your application. This service is provided for free from Postmark, the transactional email service for web apps.
For an email you received in Gmail, you can see where the email came from by looking at its headers, including how it got from the sender to the recipient's mail servers.View your email's full headers. G Suite Toolbox Messageheader