set PATH_DIR=C:\Program Files\stunnel\
set LOGSUFFX=%date:~0,2%-%date:~3,2%-%date:~6,4%
set NEWSTU=stunnel-%LOGSUFFX%.log

Net stop stunnel

@ping 127.0.0.1 -n 10 >NUL

rename "%PATH_DIR%stunnel.log" %NEWSTU%
move "%PATH_DIR%%NEWSTU%" "%PATH_DIR%logs\%NEWSTU%"

Net start stunnel