When I check my mail using “mail” it shows undelivered messages.

When I open any of the email, it gives this error.

<^>This is the mail system at host ubuntu-s-1vcpu-1gb-sgp1-01.

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

               The mail system

utsavsinghrathour@gmail.com: host gmail-smtp-in.l.google.com[172.217.194.26]
said: 550-5.7.28 [139.59.254.150 1] Our system has detected an
unusual rate of 550-5.7.28 unsolicited mail originating from your IP
address. To protect our 550-5.7.28 users from spam, mail sent from your IP
address has been blocked. 550-5.7.28 Please visit 550-5.7.28
https://support.google.com/mail/?p=UnsolicitedIPError to review our 550
5.7.28 Bulk Email Senders Guidelines. j17si92723pgj.49 - gsmtp (in reply to
end of DATA command)
<^>

What am I missing? I configured everything from the tutorials is what I believe.