Bug#670767:

[Guillaume Hoffmann]

Since darcs 2.10 [1], the command "darcs send" no longer sends an
email by default, but generates a patch bundle for later use.  It is
still possible to revert to the old behaviour with "darcs send
--mail". We kind of acknowledged that users usually don't have (or
don't want to have) an mta.

So I agree with this bug report. The darcs package should only suggest
"default-mta | mail-transport-agent" instead of recommending them.

Guillaume

[1] http://darcs.net/Releases/2.10#user-interface