Итак, я только что выполнил ниже эту команду в SSH:
openssl s_client -starttls smtp -connect smtp.sendgrid.net:587
EHLO
и получил ответ:
CONNECTED(00000005)
depth=2 C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", CN = Go Daddy Root Certificate Authority - G2
verify return:1
depth=1 C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", OU = http://certs.godaddy.com/repository/, CN = Go Daddy Secure Certificate Authority - G2
verify return:1
depth=0 OU = Domain Control Validated, CN = *.smtp.sendgrid.net
verify return:1
---
Certificate chain
0 s:OU = Domain Control Validated, CN = *.smtp.sendgrid.net
i:C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", OU = http://certs.godaddy.com/repository/, CN = Go Daddy Secure Certificate Authority - G2
1 s:C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", OU = http://certs.godaddy.com/repository/, CN = Go Daddy Secure Certificate Authority - G2
i:C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", CN = Go Daddy Root Certificate Authority - G2
2 s:C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", CN = Go Daddy Root Certificate Authority - G2
i:C = US, O = "The Go Daddy Group, Inc.", OU = Go Daddy Class 2 Certification Authority
---
Server certificate
-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----
subject=OU = Domain Control Validated, CN = *.smtp.sendgrid.net
issuer=C = US, ST = Arizona, L = Scottsdale, O = "GoDaddy.com, Inc.", OU = http://certs.godaddy.com/repository/, CN = Go Daddy Secure Certificate Authority - G2
---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA
Server Temp Key: ECDH, P-256, 256 bits
---
SSL handshake has read 5018 bytes and written 478 bytes
Verification: OK
---
New, TLSv1.2, Cipher is ECDHE-RSA-AES256-GCM-SHA384
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
SSL-Session:
Protocol : TLSv1.2
Cipher : ECDHE-RSA-AES256-GCM-SHA384
Session-ID: 081F291AEFD3E9D5396C2EF1F8579DF4DDE1C11A2CCC94CC2B668203E1D7840C
Session-ID-ctx:
Master-Key: 1A0FC6DC13AC6CBD72A1DABE175792DC0DA6F7F15D196773AC28AD0071AC71A0A9EEF680DEE76098A3E2F2EAE57D9884
PSK identity: None
PSK identity hint: None
SRP username: None
TLS session ticket lifetime hint: 300 (seconds)
TLS session ticket:
0000 - 7b 0a 89 09 92 c5 71 59-83 e9 d4 8e a8 89 cc 20 {.....qY.......
0010 - 1f bf 32 5b 69 4b 4b f1-15 b7 f4 45 24 f9 2b 38 ..2[iKK....E$.+8
0020 - 18 89 17 ee 7d 7a e1 e2-cd 27 b0 95 3e 48 c8 7c ....}z...'..>H.|
0030 - 7f fa 5c 79 a0 fd 6b e0-f7 55 f3 f4 b1 52 eb 68 ..\y..k..U...R.h
0040 - e5 be f7 02 c6 ca fe a9-7e 4f 78 fb cc 73 9c 1b ........~Ox..s..
0050 - 78 17 68 96 98 36 4b a0-7f 94 0d cf b8 ca 16 cc x.h..6K.........
0060 - 3f 1d ee 42 30 c0 b2 57-26 ed 83 72 41 0a d5 67 ?..B0..W&..rA..g
0070 - 39 9a 03 a0 b9 99 87 3f-d1 f3 ca 9a 15 46 e1 ac 9......?.....F..
0080 - 92 dd 4f 75 84 1d cd 01-01 e8 b0 6c 6d b8 41 88 ..Ou.......lm.A.
0090 - 75 73 36 13 bc e1 71 db-a7 4f 10 be 2b 23 af 61 us6...q..O..+#.a
00a0 - 7e 62 16 94 35 d7 2d f8-9e c0 db 20 b5 65 dc db ~b..5.-.... .e..
Start Time: 1584738869
Timeout : 7200 (sec)
Verify return code: 0 (ok)
Extended master secret: no
---
250 AUTH=PLAIN LOGIN
EHLO
250-smtp.sendgrid.net
250-8BITMIME
250-PIPELINING
250-SIZE 31457280
250-STARTTLS
250-AUTH PLAIN LOGIN
250 AUTH=PLAIN LOGIN
Кажется, что всё прошло успешно?!
Значит, возможно, проблема не в Digital Ocean.