The behavior of STARTTLS authentication and stream encryption (Section 10.10) can be tuned with this
TLSSrvOptions option. It is used like this:
O TLSSrvOptions=letters configuration file (V8.12 and later)
-OTLSSrvOptions=letters command line (V8.12 and later)
define(`confTLS_SRV_OPTIONS', `letters') mc configuration (V8.12 and later)
Here, letters is a list of one or more
key-letters, each separated from the next by a comma. The default is
to omit this option. As of V8.12, only one key letter is available.
It is shown in Table 24-26.
Table 24-26. TLSSrvOptions key-letters
Turn off the request for a client certificate (V8.12 and later)
The TLSSrvOptions option is not safe. If it is
specified from the command line, it can cause
sendmail to relinquish its special privileges.