Google says I am sending an unusual rate of unsolicited email and has blocked my IP address. Why? What do I do to correct and prevent this?

Google thinks that I am sending an unusual rate of unsolicited email and has blocked my IP address. Why? What do I do to correct and prevent this?
Message is “Our system has detected an unusual rate of
421-4.7.0 unsolicited mail originating from your IP address. To protect our
421-4.7.0 users from spam, mail sent from your IP address has been temporarily
421-4.7.0 rate limited. Please visit
421-4.7.0 http://www.google.com/mail/help/bulk_mail.htmlto review our Bulk
421 4.7.0 Email Senders Guidelines. e10si13212142ick.13 - gsmtp”
The email in one case was to a family member (only recipient; 3 emails same day). The second case was a ‘mass mailing’ of an article to 4 colleagues. only one of which had a gmail address.
I am using a VPN connection and a gmail account for outgoing mail. If I reset the VPN location I can start sending emails again.

Hello, what version of eM Client are you currently using on your computer, can you please check the exact release number in Help > About? I’m afraid this is not an eM Client related issue, as the high volume of unsolicited emails is detected from your IP address, this could be caused by anyone in your network as well.

Also see this article on check on options how to get removed from the Gmail’s blacklist, https://support.google.com/mail/contact/bulk_send_new?rd=1

Thank you.