Stan Hoeppner <s...@hardwarefreak.com> schrieb:

> On 6/10/2014 3:39 PM, Wietse Venema wrote:
>> Kai Krakow:
>>> BTW: In this context, what's the best approach to put mailboxes on a
>>> separate machine? Let the LDA drop mails into NFS mounts, or let postfix
>>> transport the mails via transport_map into a machine which hosts the LDA
>>> (dovecot in our case)?
>> 
>> I recommend Dovecot via LMTP, but NFS would work, too, assuming one
>> file per message. I can't say which approach would handle the most
>> load.
> 
> Dovecot's LMTP and LDA both perform index updates during delivery to the
> mailbox.  They also enable Sieve.  Dovecot's speedy performance is due
> in large part to its indexes.  If you use the Postfix LDA to drop mail
> directly into maildir files, Dovecot will need to stat the new files to
> update its indexes, before responding to a LIST command.  On a busy
> server this can be expensive, and responsiveness at the MUA may be
> sluggish.
> 
> Thus I concur with Wietse.  Use LMTP for performance, and to enable
> Sieve scripting.

Okay, thanks to both of you. That are the pointers I need. I'm currently in 
the mood of creating a new mail server architecture based on the impressions 
from the last weeks:

  * mailin server: does MX and outbound mail
  * mailout server: handle user submissions only
      * transport mails to local domains via dovecot LMTP / to mbox server
      * transport mails to remote domains by passing them to mailin server
  * bulkmail server: handle user and webserver bulk submissions
      * handles mails generated by webservers (e.g. webforms)
      * handles newsletters from worker processes
      * other bulk purposes
      * maybe handle outbound bulk mails
      * can transport to local domains directly
  * mbox server: handle pop3 and imap requests from users
      * accepts no external traffic, just from mailout / bulkmail
      * just a receiver for local domains
      * maybe handle dovecot outgoing mails (thou we didn't support anyway)

With this setup I can place different policies and rate limits for 
inbound/outbound. The mail servers mailin and mailout are named by view of 
the user altough the first handles external inbound/outbound, and the second 
handles submissions. Access to the bulk server could be limited to user 
accounts flagged as such.

Any ideas/suggestions? Do you see problems?

I'm not sure yet if I deploy this to different VM instances or just put 
multiple postfix instances on the same machine... I'd probably prefer the 
first. There's already a central and separated user db not outlined in this 
setup and accessed via mysql.

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