Some mail protocols support streaming operations. This means that PMDF
can issue more than one operation at a time and wait for replies to
each operation to arrive in batches. The
controls the degree of protocol streaming used in the protocol
associated with a channel. This keyword requires an integer parameter;
how the parameter is interpreted is specific to the protocol in use.
Currently PMDF only supports the experimental use of streaming on SMTP channels. Implementation of this feature is experimental; it may change in future PMDF releases.
The streaming values available range from 0 to 3. A value of 0 specifies no streaming, a value of 1 causes groups of RCPT TO commands to stream, a value of 2 causes MAIL FROM/RCPT TO to stream, and a value of 3 causes HELO/MAIL FROM/RCPT TO or RSET/MAIL FROM/RCPT TO streaming to be used. The default value is 0.
Some SMTP implementations are known to react badly to streaming. In particular, sendmail is known to be incapable of handling streaming levels greater than 1. PMDF's server implementation of SMTP should work properly at any streaming level.