I managed to set up a mail server, and tried to send an email to my gmail account for the first time. And I got this reply in the email log:
Our system has detected that this message is 421-4.7.0 suspicious due to the very low reputation of the sending IP address. 421-4.7.0 To protect our users from spam, mail sent from your IP address has 421-4.7.0 been temporarily rate limited. Please visit 421 4.7.0 https://support.google.com/mail/answer/188131
for more information.
Does anyone know what it is about and how to solve it? Will it unblock me after some time?