I wish for "darcs send" to support sending mail by speaking SMTP
directly to an remote MTA, in addition to the current support for
/usr/sbin/sendmail.  Below is a summary of arguments for this change.

I work from a subnotebook, which has limited volatile (RAM) and
non-volatile (SSD) storage.

One of the steps I take to reduce resource usage is to refrain from
running an MTA.  All MTAs I'm aware of either have a
permanently-running daemon (e.g. nullmailer), or simply discard
outbound mail instead of queuing it (e.g. ssmtp).

Other tools I use regularly I can configure to inject mail via SMTP
instead of /usr/sbin/sendmail, with a configurable SMTP host.  So I
simply configure them to send the mail directly to my company or ISP's
"smarthost" MTA.  This includes

    - git-send-mail (--smtp-server switch)
    - hg email (email/method in ~/.hgrc)
    - mutt (smtp_url in ~/.muttrc)
    - reportbug (-M switch)
    - bts (BTS_SMTP_HOST environment variable)
    - emacs (SMTPSERVER environment variable)

I believe it is increasingly common for laptops and workstations to
run without a local MTA.  For example, Ubuntu does not include any MTA
in its default desktop install.  Since Etch, the Debian GNU/Linux
distribution ships with an MTA installed by default, but (unlike
Sarge) is not configured during installation, and thus out-of-the-box
outbound mail is queued indefinitely.  Thus a sendmail-reliant "darcs
send" will not work "out of the box" on these distros.