I am facing the email sending problem using smtp since a couple of days back. Before that my code was working just fine. I had shifted servers and so changed my SSL certificate. After that my code has been throwing an error 500.
openssl s_client -connect smtp.zoho.com:465 -crlf
CONNECTED(00000003)
depth=1 C = US, O = "thawte, Inc.", OU = Domain Validated SSL, CN = thawte DV SSL CA - G2
verify error:num=20:unable to get local issuer certificate
verify return:0
---
Certificate chain
0 s:/CN=*.zoho.com
i:/C=US/O=thawte, Inc./OU=Domain Validated SSL/CN=thawte DV SSL CA - G2
1 s:/C=US/O=thawte, Inc./OU=Domain Validated SSL/CN=thawte DV SSL CA - G2
i:/C=US/O=thawte, Inc./OU=Certification Services Division/OU=(c) 2006 thawte, Inc. - For authorized use only/CN=thawte Primary Root CA
---
Server certificate
-----BEGIN CERTIFICATE-----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=
-----END CERTIFICATE-----
subject=/CN=*.zoho.com
issuer=/C=US/O=thawte, Inc./OU=Domain Validated SSL/CN=thawte DV SSL CA - G2
---
No client certificate CA names sent
---
SSL handshake has read 3085 bytes and written 563 bytes
---
New, TLSv1/SSLv3, Cipher is RC4-SHA
Server public key is 2048 bit
Secure Renegotiation IS supported
Compression: NONE
Expansion: NONE
SSL-Session:
Protocol : TLSv1.2
Cipher : RC4-SHA
Session-ID: 1CCFDDD21B407FC40DF9F75A692193C31A5694C0E7F9FC20CF49565FA06B81A4
Session-ID-ctx:
Master-Key: 261B3EDA6C62D65D47682F57E59CC5FBD934539D3CC3E26937A713A31CC9FEF076EC0BFC00D14ADF26095496CCA07FE1
Key-Arg : None
Krb5 Principal: None
PSK identity: None
PSK identity hint: None
TLS session ticket lifetime hint: 14400 (seconds)
TLS session ticket:
0000 - fd c6 1d 6e 29 19 0e 70-36 aa 12 f8 cd cb 4b 27 ...n)..p6.....K'
0010 - 1f 2b 83 28 e8 b0 10 4c-c9 c5 39 1d ae 94 a8 12 .+.(...L..9.....
0020 - cf 54 2d cc b7 18 39 d1-82 51 39 2c 0b 13 35 1c .T-...9..Q9,..5.
0030 - a0 ca 9a 04 8e 02 45 39-6e 96 ed 6c 23 0a 12 de ......E9n..l#...
0040 - 32 5f 78 ad c2 0d d2 86-e4 28 56 a2 5a 4e a5 1a 2_x......(V.ZN..
0050 - 32 9c a6 95 12 45 48 40-43 ab f3 d5 78 1f 58 37
2....EH@C...x.X7
0060 - 45 70 49 98 64 eb 19 ec-56 76 65 31 65 1b d6 44 EpI.d...Vve1e..D
0070 - ca 4a 1e 82 46 5e 01 a9-3f 91 19 9f 35 25 b0 53 .J..F^..?...5%.S
0080 - 1c 8c 52 b9 c5 fb bc 56-52 3f f3 cd 74 ae 44 d2 ..R....VR?..t.D.
0090 - c8 d0 ac 46 7f e8 54 6f-d7 e4 2b f0 20 8e ed 3b ...F..To..+. ..;
Start Time: 1497419239
Timeout : 300 (sec)
Verify return code: 20 (unable to get local issuer certificate)
---
220 mx.zohomail.com SMTP Server ready June 13, 2017 10:47:19 PM PDT
ehlo Zoho.com
250-mx.zohomail.com Hello Zoho.com (ec2-52-66-177-167.ap-south-1.compute.amazonaws.com (52.66.177.167))
250-AUTH LOGIN PLAIN
250 SIZE 22020096
Auth login
334 VXNlcm5hbWU6
aGVsbG9Aa2FydGFiZWQuY29t
334 UGFzc3dvcmQ6
a2FydEBiZWQyMDE0IQ==
235 Authentication Successful
traceroute smtp.zoho.com
traceroute to smtp.zoho.com (8.40.222.118), 30 hops max, 60 byte packets
1 * * *
2 * * *
3 * * *
4 100.64.16.165 (100.64.16.165) 0.274 ms 100.64.17.197 (100.64.17.197) 0.273 ms 100.64.16.165 (100.64.16.165) 0.269 ms
5 52.95.67.213 (52.95.67.213) 1.749 ms 1.722 ms 52.95.67.209 (52.95.67.209) 1.705 ms
6 52.95.66.108 (52.95.66.108) 7.445 ms 52.95.66.86 (52.95.66.86) 10.642 ms 10.625 ms
7 52.95.66.69 (52.95.66.69) 1.689 ms 52.95.66.177 (52.95.66.177) 1.656 ms 52.95.66.49 (52.95.66.49) 1.690 ms
8 115.114.89.121.static-Mumbai.vsnl.net.in (115.114.89.121) 1.914 ms 1.679 ms 115.114.89.37.static-Mumbai.vsnl.net.in (115.114.89.37) 1.811 ms
9 * * *
10 ix-ae-0-4.tcore1.MLV-Mumbai.as6453.net (180.87.38.5) 61.564 ms 61.495 ms 61.498 ms
11 * if-ae-5-2.tcore1.WYN-Marseille.as6453.net (80.231.217.29) 166.634 ms 163.559 ms
12 * if-ae-8-1600.tcore1.PYE-Paris.as6453.net (80.231.217.6) 163.525 ms *
13 * if-ae-11-2.tcore1.PVU-Paris.as6453.net (80.231.153.49) 208.487 ms 209.546 ms
14 80.231.153.66 (80.231.153.66) 243.087 ms 242.485 ms 242.470 ms
15 * * *
16 * * *
17 * * *
18 * * *
19 * * *
20 * * *
21 * * *
22 * * *
23 * * *
24 * * *
25 * * *
26 * * *
27 * * *
28 * * *
29 * * *
30 * * *
Have also attached screenshots for the above 2 steps. Please do help