One compromised mailbox can damage the sending reputation of every account you host.
WHERE TO SET IT
Max Email per Hour, defined per package and adjustable per account under WHM > Modify an Account.
WHAT TO SET
A figure that covers normal business use with room to spare, but not enough for a spam run. A few hundred per hour suits most business accounts. Increase it for a specific client who genuinely needs more.
Never set it unlimited.
WHY IT MATTERS
Outbound reputation is shared. If one account sends spam, the server address can be blacklisted, and every other client's legitimate mail starts landing in spam folders. Limits contain the damage before it spreads.
MONITORING
Watch for accounts hitting the limit unexpectedly. A client who has never sent bulk mail suddenly reaching a sending cap is almost certainly compromised, not busy.
WHAT TO TELL CLIENTS
That bulk mail must go through a dedicated provider such as SendGrid, Brevo or Mailgun, not through hosting. Say it at onboarding, because after a blacklisting it sounds like blame.
If a client needs a genuinely higher limit, raise it deliberately for that account rather than for everyone.
