[pfx] I'd like to understand this

I get two of these from double-bounce@ <mymailserver>

Return-Path: <double-bounce@<mymailserver>>
Delivered-To: gerben@<mymailserver>
Received: from <mymailserver>
 	by snape.rna.nl with LMTP
	id /fHmMkhEAWrVGAAAy+4yzw
	(envelope-from <double-bounce@<mymailserver>>)
	for <gerben@<mymailserver>>; Mon, 11 May 2026 02:51:52 +0000
Received: by <mymailserver> (Postfix)
	id CCB1FA290A; Mon, 11 May 2026 02:51:52 +0000 (UTC)
Date: Mon, 11 May 2026 02:51:52 +0000 (UTC)
From: Mail Delivery System <MAILER-DAEMON@<mymailserver>>
To: Postmaster <postmaster@<mymailserver>>
Subject: Postfix SMTP server: errors from unknown[101.47.29.67]
Message-Id: <[email protected]>

Transcript of session follows.

 Out: 220 mail.rna.nl
 In:  EHLO cangrang.cn
 Out: 250-snape.rna.nl
 Out: 250-PIPELINING
 Out: 250-SIZE 25165824
 Out: 250-ETRN
 Out: 250-STARTTLS
 Out: 250-ENHANCEDSTATUSCODES
 Out: 250-8BITMIME
 Out: 250-DSN
 Out: 250 SMTPUTF8
 In:  STARTTLS
 Out: 220 2.0.0 Ready to start TLS
 In:  EHLO cangrang.cn
 Out: 250-snape.rna.nl
 Out: 250-PIPELINING
 Out: 250-SIZE 25165824
 Out: 250-ETRN
 Out: 250-AUTH CRAM-MD5
 Out: 250-ENHANCEDSTATUSCODES
 Out: 250-8BITMIME
 Out: 250-DSN
 Out: 250 SMTPUTF8
 In:  MAIL FROM:<[email protected]>
 Out: 452 4.3.1 Insufficient system storage
 In:  QUIT
 Out: 221 2.0.0 Bye

Now, I get two of these 2 minutes apart for two different IP-addresses (one China, one Hong Kong, and this is weird too because my router should block incoming from China, that is handled by another MX) Anyway, looking in the log, I see an active spammer being rejected:

May 11 06:59:53 mymailserver smtp_haproxy/postscreen[6992]: CONNECT from [101.47.29.196]:50413 to [192.168.2.2]:25
May 11 06:59:53 mymailserver postfix/dnsblog[6993]: addr 101.47.29.196 listed by domain zen.spamhaus.org as 127.0.0.11
May 11 06:59:53 mymailserver postfix/dnsblog[6993]: addr 101.47.29.196 listed by domain zen.spamhaus.org as 127.0.0.3
May 11 06:59:53 mymailserver smtp_haproxy/postscreen[6992]: DNSBL rank 1 for [101.47.29.196]:50413
May 11 06:59:58 mymailserver smtp/smtpd[6987]: connect from unknown[101.47.29.196]
May 11 06:59:59 mymailserver smtp/smtpd[6987]: NOQUEUE: reject: RCPT from unknown[101.47.29.196]: 450 4.7.1 Client host rejected: cannot find your reverse hostname, [101.47.29.196]; from=<[email protected]> to=<[email protected]> proto=ESMTP helo=<qvwendi.cn>
May 11 06:59:59 mymailserver smtp/smtpd[6987]: disconnect from unknown[101.47.29.196] ehlo=2 starttls=1 mail=1 rcpt=0/1 quit=1 commands=5/6

This is normal stuff in my log. At some point this bad operator was rate limited. Good. But why do I get the messages from double-bounce@ in this case? And why is my postfix sending out
452 4.3.1 Insufficient system storage
if it's operating normally (receiving and sending mail and all)?

Gerben Wierda (LinkedIn <https://www.linkedin.com/in/gerbenwierda>, Mastodon <https://newsie.social/@gctwnl>, Bluesky <https://bsky.app/profile/gerbenwierda.bsky.social>)
R&A IT Strategy <https://ea.rna.nl/> (main site)
Book: Chess and the Art of Enterprise Architecture <https://ea.rna.nl/the-book/>
Book: Mastering ArchiMate <https://ea.rna.nl/mastering-archimate-edition-3-2/>
YouTube Channel <http://www.youtube.com/@GerbenWierda>

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