On Aug 11, 2010, at 3:01 PM, Tony Finch wrote:
> > On Wed, 11 Aug 2010, Arnt Gulbrandsen wrote: >> >> Some SMTP servers (even some smarthosts) will act as an SMTP client before >> replying to the dot. That was true twenty years ago (when random unix boxes >> acted as a general spool and MUAs could run e.g. sendmail -bs or smail >> -iforget to talk to an SMTP server), and it's true now. > > I think that's only true if you are running sendmail -odi (deliver > interactively option). Smail does local delivery in the foreground and > remote delivery in the background (dunno if that includes DNS lookups). > Exim can't be told to do foreground deliveries while talking to an SMTP > client, and qmail and postfix don't have the right architecture to allow > it. > > This sort of supports my earlier comment about the design of mailers > changing in this respect about 15 years ago. Spam filtering appliances and services sometimes run as, effectively, proxies rather than store-and-forward MTAs. Postini works in this way, I think, as do some of the enterprise filtering appliances that people protect their Exchange servers with. If anything, they're a more recent approach to mail filtering than their competitors that are cobbled together using the store-and-forward MTAs you mention. They have significant deployment advantages and some disadvantages. Cheers, Steve
