Email from a custom domain suddenly not received

I have a custom domain I use for email. Email to this domain is forwarded to my comcast.net email address by my domain host, godaddy. Recently (last week or two), email I send from my domain to someone on my domain is lost with no error returned. When I send to any other email address, even my comcast.net address directly, the email is received. I use smtp.comcast.net to send the mail. My domain DNS Sender Policy Framework (SPF) record is set to match the comcast.net. I receive all other email via my forwarding service, including plenty of spam, but for some reason my legitimate emails are be trashed.