I would set up Postfix as my local MTA with SASL enabled.
On an Ubuntu 9.04 example system, install the postfix, libsasl2-2 and ca-certificates packages. Create/modify the following Postfix config files.
/etc/postfix/main.cf:
biff = no
append_dot_mydomain = no
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_use_tls=yes
smtpd_tls_session_cache_database = btree:${queue_directory}/smtpd_scache
smtp_tls_session_cache_database = btree:${queue_directory}/smtp_scache
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtp_use_tls = yes
myhostname = linuxbox.int.example.com
mydomain = example.com
myorigin = $mydomain
smtpd_banner = $myhostname ESMTP $mail_name
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
mydestination = linuxbox.int.example.com, linuxbox, localhost.localdomain, localhost
relayhost = [mail.google.com]:587
mynetworks = 127.0.0.0/8
inet_interfaces = loopback-only
mailbox_size_limit = 0
recipient_delimiter = +
All other values can be defaults, in fact many of these are, of note are the smtp_* at the beginning. Change the hostname and domain for your environment.
/etc/postfix/sasl_passwd:
[mail.google.com]:587 gmail_username:gmail-password
Replace mail.google.com with whatever Google's SMTP server is and the gmail_username and gmail-password with the proper values.
Run postmap and restart postfix:
sudo postmap /etc/postfix/sasl_passwd
sudo /etc/init.d/postfix restart
Now when you send mail on your system, it will use Postfix as the local MTA and automatically authenticate with SASL.