I just upgraded inn1.4unoff3 to inn1.4unoff4 (Solaris 2.5). The following (a bit mysterious for me) sequence made the job:
config.data file as described in README:
cd config
make subst
cp config.dist config.data
./subst -f {OLDFILE} config.data, where "{OLDFILE}"
is my old config.data file.
make world
make update
cd site
make clean
make all
make diff-installed
make install
And finally I restored manually hosts.nntp and innwatch.ctl files
(I skip the latter one during diff stage - it is required to change
df to /usr/ucb/df).
Seems that now it is working...