The system is scanning the entire email for anything that might be different. This message tends to come up as well when you are using multiple "free" email addresses (like yahoo, gmail, hotmail). Most of the time, if you have checked the Message Header (the To/From) and the body of the email and they are matching, the system is reading the account email address in the footer. For example, say that your email is firstname.lastname@example.org and that is what you are using as the From, Reply To email, and have some email links within the campaign going to this address. When you set the account up though, it was set up with email@example.com; this means that the account email address is set as this hotmail address. In the footer of the email it reads " This email was sent to firstname.lastname@example.org (the contact email on the account) by email@example.com (the From email address)." The system is reading these 2 separate email addresses and giving you the Medium risk message.
To test this, and make sure this is the only reason you may be getting a medium risk on the Spam Checker, you can go to My Account > My Account and update the User Email on the account to the email address you are using as the "From" email address. When you save this in your account and go back to the email, you should be able to run the Spam Check again and not see this error message.
If you wish to keep the contact email on your account as the original address, you can go and update this information again within your account. As long as you have checked the email body for any other email addresses, then you should be safe to send your email to your audience.
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