Postfix/Dovecot setup throws "User doesn't exist" despite virtual user existing

herrbischoff

11/18/23, 7:48 PM

I have configured Postfix and Dovecot according to the documentation for virtual setups and LMTP transport:

https://www.postfix.org/VIRTUAL_README.html

/usr/local/etc/postfix/main.cf:
    virtual_transport = lmtp:unix:/path/name/to/socket 
    virtual_mailbox_domains = example.com example2.com
    virtual_mailbox_maps = hash:/usr/local/etc/postfix/vmailbox
    virtual_alias_maps = hash:/usr/local/etc/postfix/virtual

/usr/local/etc/postfix/vmailbox:
    info@example.com    whatever
    sales@example.com   whatever

/usr/local/etc/postfix/virtual:
    postmaster@example.com info@example.com

/usr/local/etc/dovecot/users:
    info@example.com:{SHA512-CRYPT}$6$/kTQFQ[...]/::::::userdb_quota_rule=*:storage=2048M
    sales@example.com:{SHA512-CRYPT}$6$/kTQFQ[...]/::::::userdb_quota_rule=*:storage=2048M

If I send emails from external addresses, it is accepted and properly transported via LMTP. Generally everything works as expected.

To remain in this example, when I send an email from sales@example.com via authenticated SMTP submission to info@example.com, it always throws:

<info@example.com>: host mx.example.com[private/dovecot-lmtp] said: 550 5.1.1
    <info@example.com> User doesn't exist: info@example.com (in reply
    to RCPT TO command)

I'm aware that the error is thrown by Dovecot's LMTP. What I don't understand is why everything works from unauthenticated external addresses but not when sending authenticated on my own.

I'm thankful for any pointers. If more configuration data is needed, let me know and I will add it.

243

1 + 2

postfix

dovecot

anx

11/18/23, 8:30 PM

There are a few ways to create unintended differences between mail submitted via *different `smtpd` instances* (rows in `master.cf`), which is preferably the case for external vs authenticated submission, I suppose it would be obvious looking at the output of the `postconf -n` and `postconf -M` commands.

herrbischoff

11/18/23, 8:51 PM

Thanks for the nudge, it is highly probable that this is the cause. I believe I have found the issue and will answer it to possibly help others in the future.

Score:1

Server

herrbischoff

11/18/23, 8:57 PM

In Postfix's master.cf there was a setting I don't remember having made:

-o receive_override_options=no_address_mappings

This, according to Postfix documentation, does what its name suggests:

Disable canonical address mapping, virtual alias map expansion, address masquerading, and automatic BCC (blind carbon-copy) recipients. This is typically specified BEFORE an external content filter.

This obviously couldn't work. Once removed it appears to work now.

+ 2

anx

11/18/23, 9:53 PM

I know very few reasons for ever using that option.. do you have any spam filtering setup to receive and then pass messages back to postfix (then that option would prevent applying rewrites & aliasing a second time)? If so, check whether you actually *do* want that option - just in a different place between initial receipt and further processing.

herrbischoff

11/18/23, 10:15 PM

Exactly, hence my confusion. I wouldn't know why I would ever use it. Spam filtering happens with rspamd via milter. Directly below was a commented-out statement regarding an approach to DKIM signing, which I ended up using an rspamd module for. My best guess is that this is part of the original approach and I just forgot to comment it out. Still, it's really weird.

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