I know the sender is good. How do I keep their email out of the spam folder?

You can find the full article here: https://www.xfinity.com/support/articles/protect-xfinity-address-book

The simplest way to make sure mail from a specific email address doesn’t go to your spam folder is by adding the sender’s email address to your Xfinity Address Book.

See Add or Edit Email Addresses in the Xfinity Address Book  for more information.

Valid emails are still going to my spam folder.
Here are some tips to prevent email you want from going to your spam folder:

• Make sure the sender’s email address is an exact match of what’s in your Xfinity Address Book.
• If you access mail from other third-party clients (such as Outlook, Thunderbird, etc.), you may need to review your settings as they have their own mail filters and blocked senders list. These filters may put the mail in the spam folder even if the sender is in your Xfinity Address Book.
• Check your email rules to make sure they aren’t moving the mail.

Note: At this time the collected address book is not utilized for spam folder protection.