I looked through RFC822 to see what it had to say on the subject.  It
doesn't specifically state that any blanks immediately following "Subject:"
should be ignored, but my reading indicates that the following should all
be considered interchangable:

>Subject:      Re: Leading blanks in Subject lines

and

>Subject:
>     Re: Leading blanks in Subject lines

and

>Subject: Re: Leading blanks in Subject lines

I base this on the section on 'folding' of header fields, which reads in part:

>   3.1.1.  LONG HEADER FIELDS
>
>      Each header field can be viewed as a single, logical  line  of
>      ASCII  characters,  comprising  a field-name and a field-body.
>      For convenience, the field-body  portion  of  this  conceptual
>      entity  can be split into a multiple-line representation; this
>      is called "folding".  The general rule is that wherever  there
>      may  be  linear-white-space  (NOT  simply  LWSP-chars), a CRLF
>      immediately followed by AT LEAST one LWSP-char may instead  be
>      inserted.
> [. . .]
>           The process of moving  from  this  folded   multiple-line
>      representation  of a header field to its single line represen-
>      tation is called "unfolding".  Unfolding  is  accomplished  by
>      regarding   CRLF   immediately  followed  by  a  LWSP-char  as
>      equivalent to the LWSP-char.

This indicates that multiple spaces are considered unimportant in mail
headers and so it's acceptable, if not required, for mail readers to ignore
them.  Of course mail readers that don't ignore them may not have the
expected results (particularly as intervening mailers may remove the spaces
without violating this RFC).

Anyone have other interpretations?  I got RFC822 from somewhere on the web
(sorry, don't remember where) so you can probably track it down pretty
easily if you want to.

-jwgh