There are numerous reasons why an email may be blocked or end up in ‘SPAM’ folder. These include how the email is formatted, the text that is present in the email, images that are embedded, as well as attachments.
To try and narrow what exactly is the cause in this situation. It is much easier to create a filter in Gmail so that any email that is being received from a particular sender does not end up in ‘SPAM’. Please select the link below for important instructions on a solution.