It may not be a "good" answer, but it might be a completely accurate one. Your headers don't show what the dealy may have been between "che" and "frida" - though you might be able to tell if you know what time the mailman program actually sent the mail.
I think there is; the DH tech should have the tools to check that, and in spite of their recent issues, they have been consistently willing to indicate where they have problems, rather than attempting to hide them.
I think you have already "isolated" the problem, as it seems to be limited to Yahoo/Hotmail - both services that, in my experience often suffer sever dealys in forwarding mail to their users' inboxes. I don't have any suggestions for a "fix", though "throttling" the amount of mail sent to them might be where I would start (though I don't know how to, or even if you can, do that with mailman).