I have 5 people that send me good email messages that always go into my spam folder. I have disables any spam enabling in settings. I have opened the messages in spam folder and mark them "not spam" but they still end up in the spam folder. Comcast is worthless in solving this.
I regret that the following does not solve the issue of good messages incorrectly being flagged as spam.
However, if it interests you it is possible to change your email settings so that spam messages are kept in the spam folder instead of being removed.
If you want to know where to go please begin from your comcast web email. While on the email page go to the upper right corner and click on the gear icon. Select "Settings" from the pull-down menu that pops up.
That takes you to the mail settings page. You’ll see a list of options in a column on the left side of the page. In that column locate and click on “Advanced Settings”. Then in the Advanced Settings window you'll find a checkbox called "Save a copy of emails marked as spam." If you select that checkbox then you should at least be able to view future messages flagged as spam in your spam folder.
I do not know if this works with mail applications like Outlook or Thunderbird.
That post is almost 18 months old and Xfinity has made changes to it's email program since then. The option that was mentioned above is no longer available which is why you don't see it.