Hector Santos wrote:
There are cases where the reply text may be longer than a
single line or the client should wait for the final response
code due to a server delayed operation. This requires a
special reply format to indicate a multiple line response or
pending final response is to be expected. This is discussed
in detail in 4.3.3 Multiple Response Lines and Timeouts.
So far I could buy it...
The final reply code has not been determined yet and
the server is performing a lengthy backend operation
which may conflict with the SMTP state machine
timeout values defined in section 4.5.3.
...but here I'm not convinced, 2821bis should NOT modify
the generous 2821 timeouts. The 123-wait (or similar)
kludge is for some impatient clients ignoring the real
timeouts. It's not for lame servers.