Update[1]:

  https://en.roquesor.com/Downloads/mail_patches.tar.gz

I've been reading more carefully the standards.  According to rfc6532,
headers can be sent directly in UTF-8, so I ended up discarding the
functions I'd written to base64 encode-word the Subject (shedding some
tears, this gave me a lot of work.)  With that, it also went away my
base64 folding function (you can't insert new lines in base64
arbitrarily.)  At least, this was a step forward regarding to what I was
told, that my diffs are too large.

But, even when rfc6532 says that now the 78 columns folding is not
longer mandatory, just cosmetic, lines are still restricted to 998
octets, which leads us to speculate the following.  Nobody needs a 998
octets Subject and even when some MUAs or MTAs generate extremely large
Message-IDs, which get accumulated in References (another header I
added to mail(1), along with Date,) you need a 20+ thread tree to exceed
that limit.  To fold or not to fold, that's the question. :-)

There already is a fmt() function included in send.c, seems to be
intended for To, Cc, and Bcc headers (defined as struct.)  So, I wrote a
new function to fold headers defined as char strings with UTF-8 support,
for now I used it to fold Subject and References.

I mean there's the option of ignoring this restriction (what can happen
is that the MTA refuses to send the mail throwing an error,) with that I
could also remove this new folding function, further simplifying my
patches.

Any advice?


       ***


(1) For the newcomers (content of ABOUT file included in the tarball):

These patches teach mail(1) to generate some headers to comply with
standards and to add necessary functionality.  Some of them, when not
generated by the MUA are added by the MTA, but it's desirable the MUA do
this so that those headers are also present in the copy of the outgoing
messages that your MUA saves locally.

This patches cannot be applied consecutively.

date.diff

  Generate User-Agent and Date.

id.diff

  Generate Message-ID, In-Reply-To, References.  Fold Subject and
  References at 72 columns.

mime.diff

  Generate MIME_Version, Content-Type and Content-Transfer-Encoding.  If
  non valid UTF-8 is detected in the body MIME headers are not generated.

all.diff

  Including all the above.