consider disabling sender verification

Users of the tails project are complaining that they cannot receive notifications from weblate server on their @torproject.org email address because of sender verification (reject_unverified_sender in Postfix). here's a part of a bounce they typically receive:

<XXXX@torproject.org>: host eugeni.torproject.org[49.12.57.136] said: 450
    4.1.7 <weblate@translate.tails.boum.org>: Sender address rejected:
    unverified address: host lizard.tails.boum.org[204.13.164.63] said: 554
    5.7.1 <weblate@translate.tails.boum.org>: Relay access denied (in reply to
    RCPT TO command) (in reply to RCPT TO command)
[ message/delivery-status ]
Reporting-MTA: dns; lizard.tails.boum.org
X-Postfix-Queue-ID: D121A4189A
X-Postfix-Sender: rfc822; weblate@translate.tails.boum.org
Arrival-Date: Thu, 17 Feb 2022 03:03:17 +0000 (UTC)

Final-Recipient: rfc822; XXXX@torproject.org
Original-Recipient: rfc822;XXXX@torproject.org
Action: delayed
Status: 4.1.7
Remote-MTA: dns; eugeni.torproject.org
Diagnostic-Code: smtp; 450 4.1.7 <weblate@translate.tails.boum.org>: Sender
    address rejected: unverified address: host
    lizard.tails.boum.org[204.13.164.63] said: 554 5.7.1
    <weblate@translate.tails.boum.org>: Relay access denied (in reply to RCPT
    TO command)
Will-Retry-Until: Tue, 22 Feb 2022 03:03:17 +0000 (UTC)
[ text/rfc822-headers ]
Return-Path: <weblate@translate.tails.boum.org>
Received: from 55e085888c8e (localhost [127.0.0.1])
        by lizard.tails.boum.org (Postfix) with ESMTP id D121A4189A
        for <XXXX@torproject.org>; Thu, 17 Feb 2022 03:03:17 +0000 (UTC)
Content-Type: multipart/related;
 boundary="===============8284330724149343160=="
MIME-Version: 1.0

we should consider disabling this check or allowing tail's weblate to bypass it.

if we do disable it system-wide, we should consider the impact it will have on incoming spam, as that probably stops a lot of abuse already... this might something we have stats on in prometheus.