When using the 'mail' or 'sendmail' options in CMSMS, the error messages about
undelivered messages may go to the administrator of the server (at least that is
what happened in my case with "mail"). If many websites are running on the same
server, then it may be preferable to direct these messages to the webmaster of
the particular CMSMS site.

Sendmail has the -f option for this purpose and specifying the sendmail path as
  /usr/sbin/sendmail -f webmaster@...
already solved the problem in my case.

Still, one might consider to handle this internally in the module, by providing
an optional "Errors-to" field. I don't know how the implementation would have to
look like for the "mail" or "smtp" options, however.
Just an idea.

Best,
Leopold