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

[Rainer Frey]

On Thursday 22 April 2010 18:15:18 Phil Howard wrote:
[ ... all standard stuff that is well documented ... ]

> 5.  Passwords stored encrypted, such as MD5.  And it should be a scheme
> that both Postfix and Dovecot can use so I don't have keep two different
> encryption schemes.

Postfix doesn't need any password directly. It only authenticates a user with 
a password in one case: SMTP SASL authentication of submission users, and it 
uses the dovecot auth service for that and does not read the password database 
itself.

> 6. I'd prefer not to, but it looks like I will have to copy data from one
> format to another format so Dovecot can read it and Postfix can read it.  I
> will most likely be using the CDB format (the constant database file format
> from Dan Bernstein ... which I'd think should be easy enough for a future
> version of Dovecot to support).

It is not about supporting a certain database library. There is simply a 
difference in what Dovecot and Postfix need from a user/recipient database. 
Dovecot needs information like path to mailbox, uid/gid with which to put 
files into the mailboxes, extra configuration fields ... Therefore it uses a 
structured  multi-value format like the passwd-file. CDB or similar don't work 
like this, so dovecot can't easily support using the same CDB files as 
postfix.

Postfix only supports name:value tables, either to use the value (table-style 
lookup) or to check whether there is an entry for a name (list-style lookup). 
Therefore it only uses file databases with such a mapping. In the case of 
valid recipients which will be handed off to dovecot for delivery, it is such 
a simple list lookup.

(If it interests you: the postfix virtual delivery agent needs very similar 
information to dovecot, but it uses several key:value maps for the different 
information, all with the recipient as key.)

> 7.  I am wondering if I can trick Postfix into reading virtual user info by
> running it chrooted where I substitute /etc/passwd and /etc/shadow with
> stuff I generate from Dovecot files.

If you need to generate the files that postfix uses, you can generate 
supported lookup table formats as well.

Rainer