All Hosting providers and ISPs must protect their servers. We use like any other provider a firewall with the almost identical rulesets. If the server picks up failures from an IP address it will block it.
The server will block your IP and remove the block again within 1 to 24 hours.
NB: Possible cause for failures are email authentication errors: This may be due to a device attempting to establish connection repeatedly with the incorrect login details. The only solution would be to confirm that the details used are correct. Blacklisted IP address would need to be delistered with the approprite providers.
We can only temporarily whitelist your IP for an hour.