It is best to debug sendmail in a window environment, within script(1), with emacs(1), or something similar. Debugging output can run to many screens.
Activities of the daemon can be observed only if the
debugging switch is combined with the others selected. This switch prevents
the daemon from disconnecting from the controlling terminal. Without
this switch, sendmail silently discards its debugging output.
Sometimes debugging output seems not to be printed:
/usr/lib/sendmail -d11.1 you < /dev/null%
When this happens, add the
-v command line switch to
keep the output attached to your screen:
/usr/lib/sendmail -v -d11.1 you < /dev/nullmany lines of output here %
There must be no space between the
-d and its numeric
arguments. If you put space there, the numeric arguments may
be interpreted as recipient addresses.