July 6, 2021 . 8 MIN READ
https://documentation.cpanel.net/display/CKB/How+to+Prevent+Email+Abuse
This document outlines some of the best practices that you can follow to avoid email abuse on your cPanel & WHM server.
If you increase the minimum password strength for your users’ mail accounts, you can decrease the chance that a hacker will correctly guess their passwords.
To define minimum password strength for all of your users’ authenticated features, use WHM’s Password Strength Configuration interface (WHM >> Home >> Security Center >> Password Strength Configuration).
Note:
We recommend that you set the default minimum password strength to at least 50.
cPHulk provides protection for your server against brute force attacks (a hacking method that uses an automated system to guess passwords). If you enable cPHulk, you can decrease the chance that a hacker can use a brute force attack to gain access to your server’s mail accounts.
To enable this feature, navigate to WHM’s cPHulk Brute Force Protection interface (WHM >> Home >> Security Center >> cPHulk Brute Force Protection) and click Off to toggle the feature’s status.
Greylisting is a service that protects your server against unwanted email or spam. When enabled, the mail server will temporarily reject any email from a sender that the server does not recognize. If the email is legitimate, the originating server tries to send it again after a delay. After sufficient time passes, the server accepts the email.
To enable this feature, navigate to WHM’s Greylisting interface (WHM >> Home >> Email >> Greylisting) and click Off to toggle the feature’s status.
If you enable the SMTP Restrictions feature, spammers cannot directly interact with remote mail servers or work around mail security settings.
mailman system user, and the root user.sendmail binary, which helps to prevent direct access to the socket.To enable this feature, navigate to WHM’s SMTP Restrictions interface (WHM >> Home >> Security Center >> SMTP Restrictions) and click Enable.
WHM’s Exim Configuration Manager interface (WHM >> Home >> Service Configuration >> Exim Configuration Manager) provides a large number of spam and abuse prevention options.
We strongly recommend that you read the Exim Configuration Manager documentation for each option in that interface.
The following settings in the Mail section of WHM’s Tweak Settings interface (WHM >> Home >> Server Configuration >> Tweak Settings) can help to prevent email abuse:
Note:
If you set the Max hourly emails per domain option to 500, this allows each of the domains that you host to send 500 email messages per hour. For example, a domain uses a mailing list with 500 members. If this domain sends a message to the mailing list, then sends another email message in the same hour, the domain will exceed the Max hourly emails per domain limit.
Use the The percentage of email messages (above the account’s hourly maximum) to queue and retry for delivery setting to specify a “soft limit.” For example, if you set the The percentage of email messages (above the account’s hourly maximum) to queue and retry for delivery value to 150, the domain can queue up to 250 messages to send in the next hour. In this scenario, the domain can queue the additional 25 email messages in the next hour.
This setting specifies the maximum number of emails that each domain can send per hour.
This setting defaults to Unlimited.
Note:
Important:
The system only enforces email send limits on remote email deliveries.
Use WHM’s Edit a Package interface (WHM >> Home >> Packages >> Edit a Package) or WHM’s Modify an Account interface (WHM >> Home >> Account Functions >> Modify an Account) to specify values for an individual package or an individual account.
To enable this setting from the command line, you must perform the following steps to manually edit the cpuser file:
/var/cpanel/users/username file, where username represents the desired account username.MAX_EMAIL_PER_HOUR key and specify the value for the selected username:
MAX_EMAIL_PER_HOUR=500 |
/usr/local/cpanel/scripts/updateuserdomains script.This setting denies the nobody user the ability to send mail to a remote address.
The setting defaults to On.
Note:
PHP and CGI scripts generally run as the nobody user. To use a PHP or CGI script to send mail, enable the suEXEC or mod_php modules in your Apache configuration.
Important:
To prevent email abuse, we recommend that you select On.
This setting specifies whether to queue outgoing messages for later delivery after a domain reaches its limit for outgoing messages per hour.
Note:
The minimum value for this setting is 100, with a maximum value of 10,000.
For example, with the default value of 125%, after the domain reaches its hourly limit Exim queues any additional messages, up to 125% of the Max hourly emails per domain value. After the account reaches 125% of the Max hourly emails per domain value, any additional outgoing messages will fail.
This setting defaults to 125%.
Note:
100.This setting allows you to specify a maximum percentage of failed or deferred messages that your domain may send per hour. Your server temporarily blocks outgoing mail from a domain if both of the following conditions are true:
The system examines all outgoing and local mail over the previous hour to determine whether these conditions are true. If only one of these conditions is true, the system does not block outgoing mail.
For more information, read our Mail Limiting Features documentation.
This setting defaults to Unlimited.
Note:
This setting specifies the initial forwarding destination for new accounts’ default/catch-all email addresses. The default address handles email that nonexistent users on your server’s domains receive.
If you receive a lot of spam at your default accounts, we recommend that you change this setting from System account (default) to Fail.
Important:
This setting changes the default setting for newly-created accounts. To change this setting for an existing account, perform the following steps:
Warning:
Do not enable suEXEC with ModRuid2. suEXEC is not compatible with this module.
If you configure PHP and suEXEC, ModRuid2, or suPHP, you can improve server security. This configuration allows you to know which users run which processes system-wide.
POSIX.1e capabilities in order to provide some performance enhancements over Apache’s default suEXEC configuration.For more information about these Apache modules, read our Apache documentation.
Any local cPanel user can use the 127.0.0.1 IP address to send mail without authentication. This can make it difficult for system administrators to determine which cPanel account sent the mail, especially when a malicious user spoofs an email address to disguise the origin of the email.
To require cPanel & WHM to put the actual sender in the header, enable the Experimental: Rewrite From: header to match actual sender option in WHM’s Exim Configuration Manager interface (WHM >> Home >> Exim Service Configuration >> Exim Configuration Manager).
After you enable this feature, you will see output that is similar to the following in the /var/log/exim_mainlog file:
2014-04-23 08:09:52 1Wcwvu-0000On-Sb From: header (rewritten was: [fakemail@example.com], actual sender is not the same system user) original=[fakemail@example.com] actual_sender=[spammer@spammer.com] |
The actual_sender portion of the log entry shows that spammer is the cPanel account that sent the email. This information allows the system administrator to take action against the account to prevent additional spam.
https://features.cpanel.net/topic/disable-email-system-for-cpanel
https://forums.cpanel.net/threads/need-help-to-stop-outgoing-email-spam.270991/
