Can I use leading zero in case of day in the Date field in SMTP

Question

Can I use leading zero in case of day in the Date field in SMTP?

I mean smth like

03 Apr 2014 13:10:22 +0000

Can you quote RFC, please?

Answer 1

There are no dates in the SMTP protocol, but you are probably referring to email header fields as described by RFC 2822 Internet Message Format. From http://www.ietf.org/rfc/rfc2822.txt we have section 3.3 Date and Time specification, with the following selected fields:

date-time       =       [ day-of-week "," ] date FWS time [CFWS]

day-of-week     =       ([FWS] day-name) / obs-day-of-week

day-name        =       "Mon" / "Tue" / "Wed" / "Thu" /
                        "Fri" / "Sat" / "Sun"

date            =       day month year

year            =       4*DIGIT / obs-year

month           =       (FWS month-name FWS) / obs-month

month-name      =       "Jan" / "Feb" / "Mar" / "Apr" /
                        "May" / "Jun" / "Jul" / "Aug" /
                        "Sep" / "Oct" / "Nov" / "Dec"

day             =       ([FWS] 1*2DIGIT) / obs-day
...

which states that the day part of the date should be between 1-2 digits, and this does not specifically prohibit using a leading zero. Nothing seems to be said about the optional leading zero, so proper interpretation should always allow it while parsing.

The obs- alternative variants describe old obsolete formats, e.g. 2-digit years and comments or folding white-space between any part.