Per https://github.com/nodemailer/nodemailer/issues/889#issuecomment-488267379 (and it’s follow-ups):
same problem here. resolved it by using IP address as host, see https://nodemailer.com/smtp/#general-options
For us it seems to be related to throttling as circa 140 messages go through in a batch while the remainder get this error (and all are being sent to the same email address, so no issue re: bad email addresses). Changing to an IP didn’t solve the issue (maybe because the SMTP is on AWS?).
What did eventually work for us was this – https://stackoverflow.com/a/55187729/235704
The below code change fixed the issue. Added this to the createTransport()
tls: {rejectUnauthorized: false}
Code:-
// create reusable transporter object using the default SMTP transport let transporter = nodemailer.createTransport({ host: 'host', port: 25, secure : false, // true for 465, false for other ports auth: { user: 'user', pass: 'password' }, tls: { // do not fail on invalid certs rejectUnauthorized: false }, });
It seems that, in our providers case, their certificates do not cover all of the IPs they are being served from on AWS.