I have the same problem I think the problem is that it works this way.
1. Your phone has some settings about how many emails to load. I can set it to 25 to 200.
2. Emails are loaded from a primary server, in this case www dot comcast.dot net. You can log in there to see your emails. Once they are deleted from THERE, they will no longer appear on your phone.
3. Emails loaded to your PC are generally downloaded and will be permanently stored there, until manually deleted. My primary email client is on my PC. It's set to delete emails from the server when they are cleared out of the deleted folder in Outlook. On my phone, it's set to leave them on the server. So when I delete it from the phone it's still on the server, and can come back when the phone email client resyncs. I don't quite know why it's not smart enough to see them in the phone's deleted folder so that it keeps reloading them. But key thing is they aren't permanently gone until deleted off the server. You should figure out when that happens for you.