Gmail blocked our Linux VPS IP address

We have a Linux VPS + Plesk with 30+ domains and many email accounts. One email account send a big number of emails to random gmail accounts and gmail block our IP. All emails from our VPS to gmail are bounced.
We fill up the google form for removing our IP from blacklist but we need a faster solution.

For example
<test[at]gmail.com>: host gmail-smtp-in.l.google.com[108.177.15.26]
said:
550-5.7.1 [213.136.69.71 12] Our system has detected that this
message
is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam
sent to
Gmail, 550-5.7.1 this message has been blocked. Please visit
550-5.7.1
https://support.google.com/mail/?p=UnsolicitedMessageError 550 5.7.1
for
more information.
e16-20020adfe390000000b00211f0bf3d59si23991783wrm.988 -
gsmtp (in reply to end of DATA command)