root@(none):~# openssl s_client -starttls smtp -connect smtp.gmail.com:587
CONNECTED(00000003)
depth=2 C = US, O = Google Trust Services LLC, CN = GTS Root R1
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
 0 s:/CN=smtp.gmail.com
   i:/C=US/O=Google Trust Services LLC/CN=GTS CA 1C3
 1 s:/C=US/O=Google Trust Services LLC/CN=GTS CA 1C3
   i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
 2 s:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
   i:/C=BE/O=GlobalSign nv-sa/OU=Root CA/CN=GlobalSign Root CA
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=/CN=smtp.gmail.com
issuer=/C=US/O=Google Trust Services LLC/CN=GTS CA 1C3
---
No client certificate CA names sent
---
SSL handshake has read 5154 bytes and written 469 bytes
---
New, TLSv1/SSLv3, Cipher is ECDHE-RSA-AES128-GCM-SHA256
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
    Protocol  : TLSv1.2
    Cipher    : ECDHE-RSA-AES128-GCM-SHA256
    Session-ID: 11E54AC1F18DF3CB294C57017B48A8D967E67FEA75367D971D9A00C7753F1C56
    Session-ID-ctx:
    Master-Key: 7E21429CFD324D407CA95721975E57D96D1597838053C05D9BF188C8B08935FE472BC9CDD42B34733E037F0D83D0F94F
    Key-Arg   : None
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 100800 (seconds)
    TLS session ticket:
    0000 - 01 05 c8 1e ee 8a 4a 1d-fc 6a cb 2c 7b 4d d4 ec   ......J..j.,{M..
    0010 - ef e7 85 f2 c4 a6 54 5e-a0 a5 ba 19 97 8d 14 07   ......T^........
    0020 - da 95 45 b1 ef 9c d4 aa-fb c9 77 53 2d d3 e3 11   ..E.......wS-...
    0030 - c0 80 f1 59 7a 7a a1 9c-b7 46 fa f6 42 71 93 60   ...Yzz...F..Bq.`
    0040 - 2a ec 54 18 cf 06 11 fa-3f 37 43 4e 06 9a ed 3f   *.T.....?7CN...?
    0050 - 78 52 f9 a2 3a c6 b7 3a-7f 94 2a 8c 2b e6 fd 5c   xR..:..:..*.+..\
    0060 - 2e 57 0e 64 0c db 5c f7-ca 98 43 8f 2f 28 b9 85   .W.d..\...C./(..
    0070 - a7 09 be 7b b3 0d 36 a7-ca d4 12 f3 48 c2 cc 8e   ...{..6.....H...
    0080 - c8 5e 35 9b 39 98 6e 32-62 bf d3 6c bf 52 cd f3   .^5.9.n2b..l.R..
    0090 - 21 7a 7b 21 6f d8 e7 b3-36 0c 86 fb 71 14 60 0a   !z{!o...6...q.`.
    00a0 - a0 cf ea fe dd f6 59 a0-e6 91 8c 9e f8 5f 71 65   ......Y......_qe
    00b0 - 25 73 7e d2 c5 59 07 63-25 78 47 4f 74 cc 8e cb   %s~..Y.c%xGOt...
    00c0 - af 84 ae 91 8f 82 96 2b-1d 41 ab 48 69 ea 34 73   .......+.A.Hi.4s
    00d0 - ea 64 ef 47 1c 9b 30 6d-b8 15 53 ab 05            .d.G..0m..S..

    Start Time: 1638955759
    Timeout   : 300 (sec)
    Verify return code: 20 (unable to get local issuer certificate)
---
250 SMTPUTF8