I really think North of 120 connections per minute is a bit much.
Not a single successful delivery too.
Shame it has no DNS.
x postfix/submission/smtpd[16485]: disconnect from unknown[52.141.56.55] ehlo=1 auth=0/1 commands=1/2
x postfix/submission/smtpd[16485]: connect from unknown[52.141.56.55]
x postfix/submission/smtpd[16485]: lost connection after EHLO from unknown[52.141.56.55]
x postfix/submission/smtpd[16485]: disconnect from unknown[52.141.56.55] ehlo=1 auth=0/1 commands=1/2
x postfix/anvil[16391]: statistics: max connection rate 107/60s for (submission:52.141.56.55) at Aug 22 16:53:42