Design Check

Felix Ingram f.ingram at
Thu Oct 28 10:29:16 EEST 2021

On Thu, 28 Oct 2021 at 00:15, <dovecot at> wrote:

> > I think your approach would work, however, if I set
> > up aliases similar to:
> >
> > -> barbaz at
> >
> > I believe I can do that in postfix with some regex magic.
> Yes, that would work perfectly without any regex.
> You just point the catchall alias to the "user".
> -> barbaz at
I've managed to get this working in postfix - I needed the regex rather
a static map, as I need to extract the unknown subdomain portion but it
to be working. I have been able to get postfix to save it to a file as well
and it seems
to work as I expected.

> [..]
> > The purpose of the system is that users can create disposable/temporary
> > email addresses for various testing jobs.
> Are you aware of postfix recipient_delimiter? It allows for disposable /
> wild card addresses. If enabled in postfix, you setup a mailbox user
> like barbaz at and any address with that user and the
> delimiter would still get delivered to that user.
>     barbaz at -> barbaz at
>     barbaz+randomtext at -> barbaz at
>     barbaz+test1 at -> barbaz at
> You can change the + to any symbol you want postfix to look out for.

We were using this approach on a different domain but our issue was that we
multiple people on the same piece of work and so they needed to share
access to
all of the mails. We decided on the approach I'm describing as we also
wanted to
have control at the DNS level to do this such as expiring addresses.

> > I think my "creating users" was me wanting to make sure that when
> > postfix
> > passes an email for "barbaz at" to Dovecot, then Dovecot will
> > store it and wait for
> > someone to come along and impersonate barbaz. i.e. "barbaz" doesn't
> > have to exist as a user
> > already before Dovecot will store the mail.
> If you are using LMTP dovecot will only accept emails from postfix that
> it can lookup the /directory/path to from one of the userdb{} or
> passdb{} sections. If dovecot can not find a match in any of the
> userdb{} or passdb{} it will reject the email as user unknown causing
> postfix to send a undeliverable notice email back to the envelope sender
> address, also known as back-scatter. I am not aware of a way to use
> wildcard addresses in dovecot userdb{}, i don't think its possible but i
> don't know what i don't know.

So I think this will be the main issue now - there's no way of knowing the
addresses ahead of time, so it sounds like I'll need to add them to
userdb{} when they
hit postfix and before they get passed to dovecot.

For my sins I'm building this on Kubernetes so dovecot is on a separate
"machine" at the
moment. The userdb will be in postgres, as I'm using that for other things,
so I guess I'll need
to update that in postfix somewhere. This is a fairly low volume system, so
I can probably take
the hit of a DB query per email.

Currently postfix doesn't even seem to be attempting to talk to dovecot but
that's one for the
postfix list.

Thanks again for the help.


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