Ensure the SMTP send recorder properly handles the recording of messages
which may have the same body hash but have different recipients. E.g.:
send the same message twice to 2 different users via Bcc.
The send recorder now maintains a list of send requests and waiting for
a message to be sent is done one the oldest of the messages.
When calculating the hash for the body to match against sent email to
avoid duplicate addition to the sent folder, do not decode the actual
contents of the body.
It is possible that certain attachments are not formed correctly but
can still accepted by the backend. Trimming spaces and \r characters is
enough to hash the message and match it later on.
This also speeds the process up as we no longer have to perform
encoding conversions.
