How to stop using gravatar

Description

I’m installing an rocket chat instance on an on-premise server, without any out-going connections to outsite,
everytime I create a new user, it took about 5 minutes to complete,
Check the log, there is an error on connecting to https://secure.gravatar.com/avatar/5a420d183a8983b6e47262e6ff665f26
How to config to stop using this gravatar?

Server Setup Information

  • Version of Rocket.Chat Server: 2.4.2
  • Operating System: Ubuntu 1804
  • Deployment Method: snap
  • Number of Running Instances: 1
  • DB Replicaset Oplog: ?
  • NodeJS Version: 8.17.0
  • MongoDB Version: 3.6.14
  • Proxy: caddy
  • Firewalls involved: N/A

Any additional Information

$ sudo journalctl -f -u snap.rocketchat-server.rocketchat-server
-- Logs begin at Mon 2020-01-20 11:32:48 +07. --
Jan 31 15:12:10 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   syscall: 'connect',
Jan 31 15:12:10 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   address: '192.0.73.2',
Jan 31 15:12:10 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   port: 443 }
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]: Error while handling the setting of the avatar from a url (https://secure.gravatar.com/avatar/5a420d183a8983b6e47262e6ff665f26?default=404&size=200) for tiendx1: { Error: connect ETIMEDOUT 192.0.73.2:443
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]:     at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1191:14)
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   errno: 'ETIMEDOUT',
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   code: 'ETIMEDOUT',
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   syscall: 'connect',
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   address: '192.0.73.2',
Feb 04 23:08:36 scpe621245be0ed rocketchat-server.rocketchat-server[687]:   port: 443 }