Comcast does not really offer a way for customers to "unspam" an email address themselves. You can select the messages in the Spam folder and click the "Not Spam" button, but it will likely take a lot of clicking on a lot of messages to change this.
If it's only happening with one or two addresses, their Security Assurance group might be able to fix this for you. Give them a call at 1-888-565-4329 (from http://constantguard.comcast.net/help/report-abuse/). Note that this is NOT one of the general customer service numbers. The first-line reps there are sometimes not very helpful. If so, be persistent, and keep at them until you get a satisfactory answer.
Without their help, the only thing you can do to prevent messages from going to the spam folder is to turn spam filtering off completely so that everything they deliver is placed in the Inbox.
Thank you for your reply. It's amazing that I've been getting emails from 2 particular sites for 2 years and now they end up in spam. I have been tagging them as not spam figuring the software would recognize that going forward but to avail. I thought adding their email addresses to my address book may have worked but to no avail. I'll give them a call. Not happy!
I have found a way to fix this:
1. Highlight the mail entry in the spam folder.
2. Instead of clicking on 'Not Spam' icon, click on 'Move' icon, next to 'Not Spam'.
3. This will bring up a 'Move' window.
4. Highlight the 'Inbox' row and check the 'Create filter rule', lower left of 'Move' window.
5. A message appears: 'All future messages from 'the email sender' will be moved to the selected folder'.
6. Click on 'Move', lower right in 'Move' window.
7. A 'Create new rule' window appears.
8. Confirm the 'Conditions' and 'Actions', make sure the 'Process subsequent rules' box is checked, lower left and click 'Save', lower right.
I tried this yesterday on one of my legit emails that was going to 'Spam'. This morning it arrived in my 'Inbox'
@braveheart46 wrote: .... 'All future messages from 'the email sender' will be moved to the selected folder'. ...
That doesn't work when I try it. I just creates an email filter that moves messages from that sender's email, and filters only run on mail delivered to the Inbox. Since Comcast delivers spam to the Spam folder and not the Inbox, filters don't act on such mail.