For signing operations it is helpful
for the signing dialog of Kleoaptra
to receive the email address
of the from-field. This way Kleopatra
could check whether this email address appears
in the default certficate or a specifically
selected certificate. If it does not appear,
a warning could be issued, because it
is usually a bad idea to sign an email
with a certificate that does not contain
the email that is written in the from-field.
Many MUAs will issue an warning when receiving and
verifying such a signed email.

Probably it is not easy to find out the from-field
in Outlook prior to sending the email.