Quoting Timo Sirainen <t...@iki.fi>:
It doesn't have to be the primary group. This is more of an Exim side problem that it doesn't assign the supplementary groups (if it did, it would have worked with dovecot-lda). I don't think the way you configured Exim to call dovecot-lda is explained anywhere in Dovecot wiki?
I'm using the exact transport from the wiki (http://wiki2.dovecot.org/LDA/Exim) but with the addition of setting user and also I have a shadow transport configured. So, yes I do have a couple of differences to what is shown in the wiki...
WRT my problem, I will work around it using primary groups or possibly abolishing the option for users/domains to use any user other than vmail. I don't think its necessary but its how I inherited this particular mail setup...
thanks for your input, cheers Andy.