Email only sending between 7pm and morning some time

What once was an intermittent issue on weekends a month or so ago has now become a daily issue: Emails sent in Apple mail (both from my MacBook and iPhone) after about 8am and before 7pm ET get parked in my Outbox with repeated SMTP server connection errors. Then 7pm comes around, and the emails get sent. No problems receiving email day or night. Comcast email is set up (box checked) to allow third party programs. No changes in my hardware or changes in my ISP. I have seen others raise this issue but have not seen a clear resolution to the problem. (No, I have no desire to set up a VPN. Yes, I can send emails if I log into Comcast and access email that way, but that is a pain and inconvenient, particularly as this has never been a problem before.) Has anyone come up with a solution that actually works (for those of us who are not techno nerds)? I have tried going through Xfinity chat multiple times, the phone multiple times, and have been kicked up to CAS but have not found anyone who can resolve this problem.