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.