Can I Mange e-mail messages on multiple computers fo Comcast Webmail?

Yes, you can.

Usually emails are downloaded from Comcast server to your local computer and once downloaded, they are removed from the Comcast server.

If you want to keep the emails on one central location (Comcast server), but view them from multiple computers,  set your e-mail program(s) to leave a copy of the message on the server.

 If you do not set it this way, all the messages from Comcast server disappear once you view them from your local computer.