Spam gets through to Outlook, but not found in xFInity app?

@rfb Outlook has its own spam filtration system in place that is seperate from the Comcast spam filtration system. Many features of outlook do not sync with the Comcast server and are unique to the client. Which is why some people prefer to use it over webmail. 

No, Comcast does its own filtering when it hits our servers, but then when it gets downloaded by Outlook - Outlook applies its own rulings ontop of it after the download.

Similarly how you could create a secondary inbox in outlook and have items once downloaded to outlook filter into the secondary inbox, but the inbox wont exist in the webmail becasue you cant have two parallel inboxes in webmail. 

Are you saying Comcast does not filter emails before they are uploaded by Outlook? Webmail is a parallel stream?

I appreciate your discussion of this issue. Wonder how you would explain what happened yesterday? While on Comcast webmail app I found a note from my doctor in their Spam folder. I marked it as “not-spam” and it was moved automatically to the webmail inbox. I then went to Outlook and it was in the inbox for the first time. So I get the impression that the xFinity spam filter is saving some spam messages to the webmail folder. But where are the others they are filtering out? Sometimes I need to view the source to see if it is spam that got all the through to my inbox on Outlook.

@rfb not sure what you are referencing to, as long as you have the spam filter enabled in Webmail - it will keep a copy of all emails marked as spam should it be selected in the settings:
https://www.xfinity.com/support/articles/spam-filters-and-email-blocking-new-experience

If I set the filter rule to discard an email from a certain address, will that rule carry forward in reading my emails in Outlook?