Skip sender check for SMTP messages

simsendmail only.
Disable SSLv2 and SSLv3
Improve SMTP receive session responsiveness

We were extremely aggressive about triggering fast queue delivery
attempts; since these are handled within the same process this made
responsiveness to some commands (including MAIL) dependent on the
speed and responsiveness of all of the remote hosts for the previous
message. Deferring these queue runs potentially lets more mail build
up, but allows us to accept mail more quickly when a client is sending
multiple messages in a single connection.
Disable message rejection in MSA mode

Causes problems for users, not core to the feature request.
Clean up logging in header parsing code

Try to always log the line we failed on, don't use perror().
Fix header caching for messages without a body

The headers were never written out due to a logic error.