Error: Can't send mail - all recipients were rejected: 501 Invalid RCPT TO address provided at SMTPConnection

[Varun Ganesh D]

I selected all unverified users in the Users section and clicked on send validation email.
on the log, I'm getting like this

2020-12-30T11:20:34.940Z [4567/20005] - error: Error: Can't send mail - all recipients were rejected: 501 Invalid RCPT TO address provided
    at SMTPConnection._formatError (/root/nodebb/node_modules/nodemailer/lib/smtp-connection/index.js:784:19)
    at SMTPConnection._actionRCPT (/root/nodebb/node_modules/nodemailer/lib/smtp-connection/index.js:1613:28)
    at SMTPConnection.<anonymous> (/root/nodebb/node_modules/nodemailer/lib/smtp-connection/index.js:1574:26)
    at SMTPConnection._processResponse (/root/nodebb/node_modules/nodemailer/lib/smtp-connection/index.js:942:20)
    at SMTPConnection._onData (/root/nodebb/node_modules/nodemailer/lib/smtp-connection/index.js:749:14)
    at TLSSocket.SMTPConnection._onSocketData (/root/nodebb/node_modules/nodemailer/lib/smtp-connection/index.js:195:44)
    at TLSSocket.emit (events.js:315:20)
    at addChunk (_stream_readable.js:295:12)
    at readableAddChunk (_stream_readable.js:271:9)
    at TLSSocket.Readable.push (_stream_readable.js:212:10)

[PitaJ]

@varun-ganesh-d that means that for at least one the unverified users, they provided an email that doesn't exist.