Comment 72 for bug 875440

Bugger I spoke too soon. It seems to have stopped working again.

I've now done as evrimfuruncu suggested and used rimap. it's far easier than banging my head against the wall.
For anyone interested my steps were;

Edit /etc/postfix/sasl/smtpd.conf so that it only conatins;

pwcheck_method: saslauthd
mech_list: plain login

Edit /etc/default/saslauthd and change these lines;

MECHANISMS="rimap"
MECH_OPTIONS="127.0.0.1"
OPTIONS="-c -m /var/spool/postfix/var/run/saslauthd -r"

Everything is now working and my system is up to date.