The wrapper script /usr/bin/stunnel3 understands stunnel3 command line
syntax and calls stunnel4 with appropriate options. It appears to
support every stunnel3 option *except* -S (which controls the defaults
used for certificate sources).
To simplify migration, /usr/bin/stunnel is a symlink to the wrapper
script. A future version will make the link point to stunnel4.
This is actually documented in the README:
The wrapper script /usr/bin/stunnel3 understands stunnel3 command line
syntax and calls stunnel4 with appropriate options. It appears to
support every stunnel3 option *except* -S (which controls the defaults
used for certificate sources).
To simplify migration, /usr/bin/stunnel is a symlink to the wrapper
script. A future version will make the link point to stunnel4.