could not setup dkim in nodemailer - node.js

Question

I want to setup DKIM in nodemailer. Without DKIM, tls and "secure: true" my code works fine however, when I run code changed for DKIM it shows error:
Code:
var nodemailer = require('nodemailer');
var fs = require("fs");
const pr_key = fs.readFileSync("private.key", {encoding: "utf-8"})
const transporter = nodemailer.createTransport({
port: 465, // Postfix uses port 25
host: 'example.com',
secureConnection: false,
tls: {
ciphers:'SSLv3'
// rejectUnauthorized: false
},
secure: true,
dkim: {
domainName: "mail.example.com",
keySelector: "mail",
privateKey: pr_key
},
auth: {
user: "abc",
pass: "def"
},
});
var message = {
from: 'noreply#example.com',
to: 'pleasereply#example.com',
subject: 'Confirm Email',
text: 'Please confirm your email',
html: '<p>Please confirm your email</p>'
};
transporter.sendMail(message, (error, info) => {
if (error) {
return console.log(error);
}
console.log('Message sent: %s', info.messageId);
});
Error Message:
[Error: 7336:error:1408F10B:SSL routines:ssl3_get_record:wrong version
number:c:\ws\deps\openssl\openssl\ssl\record\ssl3_record.c:332: ] {
library: 'SSL routines', function: 'ssl3_get_record', reason:
'wrong version number', code: 'ESOCKET', command: 'CONN' }
I have already configured TXT record for DKIM in DNS and SMTP server running on my server side is programed using library "smtp-server" module of nodejs.
What I tried:
I tried changing port to 25, 2525, 465 and 143
Tried every combination of host, domainname for domain "example.com" and tried keySelector "mail" and "#".
I tried commenting "secureConnection" and "tls: {}" and then changing to "secure: false" which results in other error:
Error: self signed certificate
at TLSSocket.onConnectSecure (node:_tls_wrap:1530:34)
at TLSSocket.emit (node:events:526:28)
at TLSSocket._finishInit (node:_tls_wrap:944:8)
at TLSWrap.ssl.onhandshakedone (node:_tls_wrap:725:12) { code: 'ESOCKET', command: 'CONN' }
i tried to change "to:" property of message object to my gmail account just for testing but still got same message saying I got wrong version
Help me resolving this issue.