upstream (gmail-smtp-in.l.google.com.) temporary error: Unknown error: transient error (421): 4.7.28 Gmail has detected an unusual rate of unsolicited mail. To protect 4.7.28 our users from spam, mail has been temporarily rate limited. For 4.7.28 more information, go to 4.7.28 https://support.google.com/mail/?p=UnsolicitedRateLimitError to 4.7.28 review our Bulk Email Senders Guidelines.
The guidelines in this article can help you successfully send and deliver email to personal Gmail accounts. Starting in 2024, email senders must meet the requirements described here to send email to G