RE: Activation points and callout modes

An implementation can certainly cache a message during simultaneous
receive/send and defer storage until it is clear that the delivery
won't complete?

Tony Finch on Wed, 2 Feb 2005:

>  I doubt any proper MTAs work in this way, but some firewalls implement
>  SMTP proxies (pejoratively known as "SMTP fux-up mode" because of the
>  gratuitous incompetence of many implementations). These are probably in
>  the target area for OPES.

>  > And how many try a direct forward and store only if that does not work out?

>  I don't think there are any. That would imply attempting to do a
>  complete delivery of the message to its next hop in the time between
>  CRLF.CRLF and its response, which is against the following text from RFCs
>  1123 and 2821:

>     To avoid receiving duplicate messages as the result of timeouts, a
>     receiver-SMTP MUST seek to minimize the time required to respond to
>     the final <CRLF>.<CRLF> end of data indicator.  See RFC 1047 [28] for
>     a discussion of this problem.