Mail was the suffix given to earlier long run express trains meant for postal transferring coaches, apart fom pasenger boggies, mostly pre-indepedence, as nowdays o new trainnamed as mail.
These trains were prioritized high because of postal urgencies.
Express are the same suffix given to trains in recent time, with less difference.
Now postal service doesnt depend on Mail/Express suffix, as Punjab Mail no...
more... more have RAIL MAIL coach, while HWH ASR express do have.
Agan now, mail are supposed to be slower compared to SUPEFAST OR EXPRESS, cz they are too old with lots of induced stoppages & if the mail isnt superfast, then its worthless (Barauni mail)