SmtpClientPreferSendAsBinaryData Property

protected virtual bool PreferSendAsBinaryData { get; }

Property Value

Gets whether or not the BDAT command is preferred over the standard DATA command.

The BDAT command is normally only used when the message being sent contains binary data (e.g. one mor more MIME parts contains a Content-Transfer-Encoding: binary header). This option provides a way to override this behavior, forcing the SmtpClient to send messages using the BDAT command instead of the DATA command even when it is not necessary to do so.

Reference