“No worthy mechs found” when trying to relay email to Gmail using Postfix

I've been trying to configure email to forward to Gmail, using Postfix to relay email to smtp.gmail.com. However, I'm failing to get it to authenticate with smtp.gmail.com, which is a rather vital prerequisite to getting anything working…

The mail logs show only:

Oct 29 15:50:14 gsnedders-1 postfix/master[6596]: daemon started -- version 2.7.1, configuration /etc/postfix
Oct 29 15:50:19 gsnedders-1 postfix/pickup[6598]: EBA1F78750: uid=1000 from=<gsnedders>
Oct 29 15:50:19 gsnedders-1 postfix/cleanup[6603]: EBA1F78750: message-id=<20111029145019.EBA1F78750@mail.gsnedders.com>
Oct 29 15:50:19 gsnedders-1 postfix/qmgr[6599]: EBA1F78750: from=<gsnedders@gsnedders.com>, size=324, nrcpt=1 (queue active)
Oct 29 15:50:19 gsnedders-1 postfix/cleanup[6603]: F2D557874F: message-id=<20111029145019.EBA1F78750@mail.gsnedders.com>
Oct 29 15:50:19 gsnedders-1 postfix/local[6605]: EBA1F78750: to=<me@gsnedders.com>, orig_to=<me>, relay=local, delay=0.04, delays=0.03/0.02/0/0, dsn=2.0.0, status=sent (forwarded as F2D557874F)
Oct 29 15:50:19 gsnedders-1 postfix/qmgr[6599]: F2D557874F: from=<gsnedders@gsnedders.com>, size=454, nrcpt=1 (queue active)
Oct 29 15:50:19 gsnedders-1 postfix/qmgr[6599]: EBA1F78750: removed
Oct 29 15:50:20 gsnedders-1 postfix/smtp[6606]: warning: SASL authentication failure: No worthy mechs found
Oct 29 15:50:20 gsnedders-1 postfix/smtp[6606]: F2D557874F: SASL authentication failed; cannot authenticate to server smtp.gmail.com[74.125.157.108]: no mechanism available

And the postfix config is:

relayhost = [smtp.gmail.com]:587

smtp_use_tls = yes
smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl/passwd
smtp_sasl_security_options = noanonymous

smtp_tls_eccert_file =
smtp_tls_eckey_file =
smtp_tls_security_level = may
smtp_tls_CAfile = /etc/postfix/cacert.pem
smtpd_tls_received_header = yes
tls_random_source = dev:/dev/urandom
smtpd_tls_security_level = may