Playing with my dispatcher configuration (openser-1.2.1) I discovered that ds_select_dst() crashes openser when dispatche param ds_use_default is set to 1 and the set from where the destination is picked up contains just one address. This appens because in dispatch.c at row 784 the code is

if(ds_use_default!=0)
                hash = hash%(_ds_list[idx].nr-1);
        else
                hash = hash%_ds_list[idx].nr;

so if ds_use_default is set and the address set has 1 destination the % causes a crash.
To avoid this it's enough to modifiy the if statement like:

if (ds_use_default!=0 && _ds_list[idx].nr!=1)

Just my two cents.
Regards,
Federico
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Federico Cabiddu

Federico Cabiddu R&D Software Engineering
Abbeynet S.p.A. - www.abbeynet.com

phone: +39 070 2339349