Hi,

└─# openssl s_client -connect mx.clean-mailbox.com:25 -starttls smtp
CONNECTED(00000003)
depth=2 C = US, O = Internet Security Research Group, CN = ISRG Root X1
verify return:1
depth=1 C = US, O = Let's Encrypt, CN = R3
verify return:1
depth=0 CN = clean-mailbox.com
verify return:1
---
Certificate chain
 0 s:CN = clean-mailbox.com
   i:C = US, O = Let's Encrypt, CN = R3
   a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256
   v:NotBefore: Sep 12 07:45:16 2023 GMT; NotAfter: Dec 11 07:45:15 2023 GMT
 1 s:C = US, O = Let's Encrypt, CN = R3
   i:C = US, O = Internet Security Research Group, CN = ISRG Root X1
   a:PKEY: rsaEncryption, 2048 (bit); sigalg: RSA-SHA256
   v:NotBefore: Sep  4 00:00:00 2020 GMT; NotAfter: Sep 15 16:00:00 2025 GMT
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=CN = clean-mailbox.com
issuer=C = US, O = Let's Encrypt, CN = R3
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 3383 bytes and written 439 bytes
Verification: OK
---
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---
250 CHUNKING
---
Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384
    Session-ID: 00D6CAA4EE949C3557B08565B51D7C6306178845943C34DC22813BAD705EE3C4
    Session-ID-ctx:
    Resumption PSK: B6A07E5E0CDE73C09258D47D7BCE560F692F84D0FAECEA0C708BBD23AD8E0F32EAD86A72896612D2E9E1F5DA13E5225F
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 7200 (seconds)
    TLS session ticket:
    0000 - 8f ba 03 a8 ee 0a 5b 26-95 94 a2 1b 97 cb 15 b9 ......[&........
    0010 - 7e f4 94 66 cd df f1 3a-98 f7 12 45 fd d3 ef 09 ~..f...:...E....
    0020 - 0b be ba bd 6f 67 ea 22-5e 3e 2d 27 09 45 ff ad ....og."^>-'.E..
    0030 - cf 5c 10 3f 28 c6 ad 89-4e df 6a 8e 43 1a 0d 1e .\.?(...N.j.C...
    0040 - 9d 88 58 e3 52 93 76 c2-98 41 06 b7 e8 7c 97 3a ..X.R.v..A...|.:
    0050 - 2b a5 08 aa d1 25 da 8e-0c 71 38 bc d4 5f 60 26 +....%...q8.._`&
    0060 - be 09 9e af f5 71 78 42-92 e2 e4 e7 6b 36 b7 98 .....qxB....k6..
    0070 - ea 09 38 be 96 44 60 ed-90 06 5b 28 ca 1f 8e 70 ..8..D`...[(...p
    0080 - e5 fe 1e 8c 49 8a 0c 53-3b 8d 56 0b ed 15 d3 af ....I..S;.V.....
    0090 - 61 d6 fb 2d 72 1f 4c 74-c6 3e 1f 52 b7 90 11 45 a..-r.Lt.>.R...E
    00a0 - 31 09 68 e5 51 73 30 05-e9 01 d8 4c 50 8d 25 e8 1.h.Qs0....LP.%.
    00b0 - a0 0b f9 12 fe 4d bd 61-65 24 f3 8e b0 82 a1 f2 .....M.ae$......
    00c0 - 69 26 69 a9 3d e9 c8 6f-ab 46 8b 20 fc 2e e8 f4 i&i.=..o.F. ....
    00d0 - cf 54 b5 70 c5 24 70 0d-f7 29 82 b1 2e 42 c5 1b .T.p.$p..)...B..
    00e0 - b9 08 71 2a f8 4e bc b0-69 d7 b6 f6 cc 32 88 55 ..q*.N..i....2.U

    Start Time: 1694514461
    Timeout   : 7200 (sec)
    Verify return code: 0 (ok)
    Extended master secret: no
    Max Early Data: 0
---
read R BLOCK

Camille

Le 12/09/2023 à 12:21, Ken O'Driscoll via mailop a écrit :

What do you see when you run openssl s_client -connect… against the the MTAs that are associated with this specific error in your logs?

Ken.


On 12 Sep 2023, at 10:50, Camille - Clean Mailbox via mailop <mailop@mailop.org> wrote:

Ok I'm now running RSA without DST cert:
# openssl crl2pkcs7 -nocrl -certfile /etc/letsencrypt/live/clean-mailbox.com/fullchain.pem <http://clean-mailbox.com/fullchain.pem>| openssl pkcs7 -print_certs -noout
subject=CN =clean-mailbox.com <http://clean-mailbox.com/>
issuer=C = US, O = Let's Encrypt, CN = R3

subject=C = US, O = Let's Encrypt, CN = R3
issuer=C = US, O = Internet Security Research Group, CN = ISRG Root X1

Still:

2023-09-12T10:48:56.708719+02:00 mx2 postfix/smtpd[406672]: SSL_accept error fromm240-158.my-hammer.de <http://m240-158.my-hammer.de/>[159.112.240.158]: -1 2023-09-12T10:48:56.710166+02:00 mx2 postfix/smtpd[406672]: warning: TLS library problem: error:0A000412:SSL routines::sslv3 alert bad certificate:../ssl/record/rec_layer_s3.c:1586:SSL alert number 42:

Camille

Le 12/09/2023 à 10:15, Slavko via mailop a écrit :
Ahoj,

Dňa Tue, 12 Sep 2023 09:25:59 +0200 Geert Hendrickx via mailop
<mailop@mailop.org> napísal:

The reason is likely the certificate itself, not the chain; this
server offers (only) an ECC certificate, and while the vast majority
of clients are compatible with this today, some still only support
RSA.
Yes, i can confirm this. My MX's stats shows that one sender still
requires RSA. Unfortunately it is my bank, thus i use dual certs ;-)

In other words, the MX is only one my service with dual certs. When i
start to use EC, i had dual certs for MSA too, but after some time, i
abandon the RSA, as all clients was happy with EC...

regards


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