Ich weiß nicht, wo Du nachgeschaut hast, aber ein Datumsfeld in einer "Internet"-Mail muss folgendes Format haben: 3.3. Date and Time Specification
Date and time occur in several header fields. This section specifies
the syntax for a full date and time specification. Though folding
white space is permitted throughout the date-time specification, it
is RECOMMENDED that a single space be used in each place that FWS
appears (whether it is required or optional); some older
implementations may not interpret other occurrences of folding white
space correctly.
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
time = time-of-day FWS zone
time-of-day = hour ":" minute [ ":" second ]
hour = 2DIGIT / obs-hour
minute = 2DIGIT / obs-minute
second = 2DIGIT / obs-second
zone = (( "+" / "-" ) 4DIGIT) / obs-zone
Also nix mit März, das ist eindeutig ein Fehler in der Config - IMHO.