Gmail SMTP error - Temporary block?

Question

I am using Gmail servers to send email from my system, with a program. Recently I started getting errors like this:

Data command failed: 421 4.7.0 T

Answer 1

I too had the same issue when I tried to send bulk emails using the multi threaded program in Java. Then I heard about Thread Pool Executor. I used it by setting Thread Pool size as 10. After that, this issue has been solved for me.

Answer 2

This error occurs if you are using scripts to send emails in quick successions. An easy way out is to apply a sleep timer in between sending emails.

I applied a timer for 1 second between each successive email.

import time
time.sleep(1) // equivalent to 1 second sleep

Answer 3

If you are using your free Gmail account to send bulk emails your are likely to see this kind of responses early on as the service is not intended to send application transaction messages, newsletters etc., event to subscribers that has opted in. The IMAP/SMTP service provided is for you to be able to use an email client like Microsoft Outlook with your Gmail account.

If you need to send transaction messages, I suggest you google "AWS SES" for starters.