Thanks to you Dan I have auth working directly with MySQL without pam_mysql. Now that I can see something working and can follow more specific google queries I see that this approach is limited to storing clear text passwords. Using pam_mysql offers a couple of extra crypted options but still nothing like Dovecots SHA512-CRYPT so I guess I'll eventually look into using Couriers authdaemond to see what it offers (I used to use the full Courier suite 10 years ago).
BTW the main thing that confused me with various examples was the use of, for instance, pwcheck_method: in smtpd.conf vs sasl_pwcheck_method: in imapd.conf with and without the sasl_ prefix. Now that I have some working configs it makes sense but not when looking at various, and quite old, howto examples. In fact I don't think I came across any howto example that showed step by step exactly how to do this.
