Note : cpanel versions 11.X differs from their predecessors’ behaviour.

Tried once : vi /var/cpanel/cpanel.config and change entry “maxemailsperhour=200” as you wish.

you can change the default maximum emails per hour by updating the file via SSH accessing the server.

[root@server ~]#vi /var/cpanel/maxemailsperhour

or

/var/cpanel/maxemailsperdomain

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You can change from path /var/cpanel/users/username for particular user.
or
From whm tweak settings(for all)
or
from whm, “configserver mail manage” plugin.