Please provide more details. Are you saying that ALL emails in your Inbox are gone?
Have you checked your Settings under the Gear icon on the far left?
Open Xfinity Connect. On the far right side of the page, click on the ‘gear’.
This is where you will find all of your Settings...check each
Also look at how much space you currently have. The limit is 10 Gigs. I highly doubt you have exceeded the limit unless you have hundreds of emails in your Inbox as well as attachments.
In addition to Xfinity Connect, do you also use an email client or smart phone?
Eg. Outlook, Safari Mail,etc. if you do, and use the IMAP settings, when you delete an email there, the email will also be deleted from Xfinity Connect.