[Dovecot] Why deliver+usercheck? deliver+MTA?

[Timo Sirainen]

On Wed, 2010-10-13 at 22:42 +0200, Lukas Haase wrote:
> > It's Postfix related - Dovecot does no checks about valid recipients
> > for Postfix but you can use the same data sources as for Dovecot - no
> > need to maintain user lists for Postfix and Dovecot.
> 
> But *why* would you want to let dovecot (deliver) check this?
> 
> In any reason the MTA *must* have validated the existance of the local 
> part. I do not know any reason why deliver should do this.

When running deliver -d the main point is that you're telling it to do a
userdb lookup. The lookup's main point is then to get the necessary
information where and how to deliver the mail, it's not just about doing
a "does user exist?" check. If you don't specify -d parameter, there is
no user existence lookup done.

But yeah, the wiki pages should talk about backscatter. Would be nice if
someone updated the pages giving some examples (e.g. sql) how to
configure Postfix, etc. to do the lookup.