dovecot - Oct 2021 - Design Check

On Wed, 27 Oct 2021 at 18:27, <dovecot at ptld.com> wrote:
> > On 10-27-2021 12:06 pm, Felix Ingram wrote:
> >
> > user1 at foobar.mydomain.com
> > user2 at foobar.mydomain.com
> > user1 at barbaz.mydomain.com
> > user2 at barbaz.mydomain.com
> >
> > I would like all emails to the "foobar" subdomain to end up
in their
> > own mailbox and all emails to the "barbaz" subdomain to go
to their own
> > mailbox.
>
> Your question might be more suited to the postfix mailing list. Dovecot
> doesn't receive mail from the internet, which i believe you understand
> as you said "have postfix accepting the emails before passing them to
> Dovecot".
>
> On the postfix side, one option would be using one mailbox and one
> catchall for each subdomain.
>
>     Setup a user: catchall at foobar.mydomain.com
>     Setup an alias: @foobar.mydomain.com -> catchall at
foobar.mydomain.com
>
>     Setup a user: catchall at barbaz.mydomain.com
>     Setup an alias: @barbaz.mydomain.com -> catchall at
barbaz.mydomain.com
>
> On the dovecot side, you can setup each person with their own login user
> and all of those users access the same IMAP inbox. Or you could just
> give everyone the password to the same one mailbox
> catchall at foobar.mydomain.com.
>
>
So I think this would make sense, though one stumbling block could be that
we don't
know the various subdomains ahead of time. The purpose of the system is
that users
can create disposable/temporary email addresses for various testing jobs.
The subdomain
can be any value that the user wants, and we don't want them to have to
precreate them before
they can use an address (we have an existing system that works this way,
and so we want to
keep that behaviour). I think your approach would work, however, if I set
up aliases similar to:

@barbaz.mydomain.com -> barbaz at mydomain.com.

I believe I can do that in postfix with some regex magic.
I would then want users to log in as "barbaz", and get access to all
of the
emails. I believe that
if I create Dovecot users for my system users, and then set them as master
users, then they will
be able to log into Dovecot with something like:

barbaz*<system user account>

as their username.


Not sure "dovecot creating users" is the right way to think about
it.
> Dovecot simply looks for IMAP files where its told to look. In dovecot
> config you setup flat files or databases that tell dovecot if someone
> logs in with this user:pass then look in this /server/path for emails.
> Other than that config, which you could point to a different
> /server/path changing their inbox, there are no "accounts".
>
I think my "creating users" was me wanting to make sure that when
postfix
passes an email for
"barbaz at mydomain.com" 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.

Thanks again for the pointers - I shall play with postfix local delivery
before trying to wire up Dovecot.

Regards,

Felix
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> I think your approach would work, however, if I set
> up aliases similar to:
> 
> @barbaz.mydomain.com -> barbaz at mydomain.com.
> 
> 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.mydomain.com -> barbaz at mydomain.com


> one stumbling block could be that we don't
> know the various subdomains ahead of time.
> 
> The subdomain can be any value that the user
> wants, and we don't want them to have to
> precreate them before they can use an address
Best to my knowledge this is not possible with postfix. But ask the 
postfix mailing list to get a definitive answer. In postfix you have to 
tell it the domains it accepts mail for, anything else it considers 
relaying. Otherwise how does postfix know that email is meant to be 
saved here or it is just passing through and you want postfix to query 
DNS to find out where it goes (if relaying is even allowed).


> 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 mydomain.com and any address with that user and the 
delimiter would still get delivered to that user.

    barbaz at mydomain.com -> barbaz at mydomain.com
    barbaz+randomtext at mydomain.com -> barbaz at mydomain.com
    barbaz+test1 at mydomain.com -> barbaz at mydomain.com

You can change the + to any symbol you want postfix to look out for.


> I think my "creating users" was me wanting to make sure that when
> postfix
> passes an email for "barbaz at mydomain.com" 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.