Email sending limits and spam protection in WHM

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cPanel can limit how many emails each domain sends per hour. Limits stop a hacked website or email account from sending thousands of spam emails. Spam like that gets the server's IP address blacklisted, and then email from every account on the server stops being delivered.

Reseller hosting

On our reseller servers we set an hourly sending limit for every domain and watch outgoing email for spam. If a domain reaches its limit, extra messages wait in the queue and are sent later.

  • To check whether a message was delivered, use Email > Mail Delivery Reports in WHM.
  • For newsletters and other bulk email, we recommend a dedicated email marketing service rather than your hosting account.
  • If one of your clients needs a higher limit, please open a support ticket.

Every account also has cPanel's own spam filters. See Spam Filters in cPanel's documentation.

Your own server (cloud or dedicated)

If you haven't set a limit on your server yet, we recommend doing so.

Set a limit for the whole server

1. Log in to WHM as root and go to Server Configuration > Tweak Settings.

2. Click the Mail tab.

3. In Max hourly emails per domain, enter a limit that's higher than your busiest legitimate sender needs, for example 500.

4. Click Save.

The same tab has two related settings that help catch spammers early: Maximum percentage of failed or deferred messages a domain may send per hour, and Monitor the number of unique recipients per hour to detect potential spammers.

Set a limit for one account

To give one account a lower limit than the rest of the server, go to Account Functions > Modify an Account, select the account, and set Maximum Hourly Email by Domain Relayed. To set it for every account on a package, edit the package in Packages > Edit a Package.

Stop scripts from going around the mail server

Malicious scripts sometimes connect straight to other mail servers to send spam, bypassing your limits. SMTP Restrictions blocks this, so only the mail server can send email.

1. In WHM, go to Security Center > SMTP Restrictions.

2. Click Enable.

If your server uses the CSF firewall, use either its SMTP_BLOCK option or WHM's SMTP Restrictions, not both.

Block incoming spam

  • RBLs (real-time blocklists) reject email from servers known to send spam. In WHM, go to Service Configuration > Exim Configuration Manager, and on the RBLs tab turn on the Spamhaus and SpamCop lists. You can add others, such as the Barracuda list, which requires free registration at barracudacentral.org first. RBLs only work if your server looks up DNS with its own resolver, not a public one such as 8.8.8.8.
  • Spam filters in each cPanel account move or delete messages that look like spam.

For stronger filtering of incoming email, we also offer SpamExperts spam filtering. See Account Upgrades.

For all mail settings, see cPanel's Tweak Settings: Mail, SMTP Restrictions and Exim Configuration Manager documentation.

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