[Dovecot] best choice of user database file to work with postfix

[Phil Howard]

On Thu, Apr 22, 2010 at 3:12 PM, Stan Hoeppner <stan at hardwarefreak.com>wrote:

> With this many lookup table types supported by Postfix, is it true that it
> has no "simple" table type in common with Dovecot?
>

There are some ... like mysql for example.  The ones I call "simple" are
ones that have a single file in some readily contructable form.  These
include btree (Berkeley DB) and cdb (Dan B's CDB).  Others could be included
but I haven't looked at them, yet (such as cidr, which has specific
purposes, only).  Things I consider "not simple" involve making a network
connection.  It can certainly be simple to configure them.  But I'm
classifying these in terms of the number of things going on to get the
answer.  Even a DB scheme to use a DNS lookup (not implemented for Postfix)
I would consider as "not simple" here, even though it is likely very simple
to do.  The tcp scheme is probably the simplest of the network schemes (but
it requires something to listen somewhere).  If I were asked what I think
could be added to this list of lookup schemes, it might be a long, long
thread.  Let's not do that here.

             unix (read-only)
>                     A  limited way to query the UNIX authentica-
>                     tion  database.  The  following  tables  are
>                     implemented:
>
>                     unix:passwd.byname
>                            The  table is the UNIX password data-
>                            base. The key is a login  name.   The
>                            result  is  a  password file entry in
>                            passwd(5) format.
>
>                     unix:group.byname
>                            The table is the UNIX group database.
>                            The  key is a group name.  The result
>                            is a group  file  entry  in  group(5)
>                            format.
>

This is "simple", too.  But the problem is it isn't flexible enough.
Dovecot supports this scheme and can use it on any specified file.  Postfix
is limited to just the system files (and is probably using Unix library
calls to access it, hence the source of the limitation).

I would think the general (insert some character here)-separated file should
be doable:
    comma-delimited:/some/file/name
    colon-delimited:/some/file/name
    tab-delimited:/some/file/name
    space-delimited:/some/file/name
But it hasn't been done that I can see (some third party patch not
withstanding).

Anyway, I need to re-study what is involved with the virtual users, since I
may have to be doing this in Postfix just to get submission authentication
to work, and then see how that affects using local_recipient_maps.  And at
this point it's probably more of a SASL issue than a Dovecot issue.  So back
to reading Postfix docs (including the SASL reference someone gave) and
asking on the Postfix M/L if needed (not here, this is for Dovecot).  It may
well be the description given early to use Dovecot SASL to authenticate
Postfix submission users would be just fine, as long as Postfix does a SOFT
rejection when Dovecot isn't up, so it requeues files.  On the SMTP end, I
just want an up front rejection decision to avoid backscatter.  The one
backscatter hole where an existing user is being deleted while incoming mail
is being queued is probably insignificant.