Please ignore my previous question.. as it turns out it's a bug/feature of fprintf(3C) and sockets under Solaris.

Exim was using fprintf to output the AUTH string and for some unknown reason it was hanging, possibly because the input buffer on the file stream wasn't empty or something.

After modifying the Exim's dovecot authentication plug-in to use write(2) instead of fprintf(3C) it miraculously worked!

Steve

Computer Systems Administrator, E-Mail:-steve@earth.ox.ac.uk Department of Earth Sciences, Tel:- +44 (0)1865 282110 University of Oxford, Parks Road, Oxford, UK. Fax:- +44 (0)1865 272072