In earlier days,few trains used to have Mail Service,since Railways was a faster mode of travel and mails used to reach quickly. Now, most of the mails are sent y airplanes or through road transport. However,due to increasing demand, RMS Coaches of many mail trains have been discontinued and reserved coaches are attached. However few trains like 11027/28 still has RMS coaches. There is no basic difference now between a mail train and express train.