To send patch bundles directly from darcs using the command darcs send --mail you need to have some sendmail program configurated. msmtp enables you to use a third-party mail acccount to do so (gmail for instance).

Under Ubuntu you will need the packages msmtp-mta and ca-certificates.

You will need to create a configuration file ~/.msmtprc. Here is mine to use with gmail (on my Ubuntu box):

port 587
tls on
auth on 
syslog on
tls_trust_file /etc/ssl/certs/ca-certificates.crt

You can put your password directly in that file but I’d rather not. This means each time you’ll do darcs send --mail you’ll be prompted for your gmail password.

The ~/.msmtprc file needs to have permissions set to 0 for group and others, otherwise msmtp will refuse to send any mail.