With mail you can say 'you are on a restricted network, use smtp server foo as relay, everything else will be blocked' (and then the user can choose to use the relay or not, and the relay can choose to relay or not depending on its settings)
With http you have to MITM to get the same result.
Posted Jan 29, 2013 13:49 UTC (Tue) by khim (subscriber, #9252)
[Link]
With http you have to MITM to get the same result.
If you don't want to open encrypted message then simple routing rule will be enough and there are proxy autodiscovery mechanisms, if you do want to open encrypted message then you must somehow convince me to replace key in my PGP or S/MIME client - the same as with HTTPS.
So I can not see the difference. Well, except for one: you need to specify relay for the mail, while proxy can be autodiscovered. I don't think it such a big difference.