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Ways to Prevent Email Abuse

Certain best practices need to be followed in order to ensure that email abuse on cPanel & WHM server can be avoided.

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Ways to Prevent Email Abuse

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  1. Ways to Prevent Email Abuse

  2. Table of Contents • Max Hourly Emails Per Domain (Continued) • Account-Specific Max Hourly Emails Per Domain Settings • Prevent “nobody” from Sending Mail • The Percentage of Email Messages (above the Account's Hourly Maximum) to Queue and Retry for Delivery • Maximum Percentage of Failed or Deferred Messages a Domain May Send Per Hour • Maximum Percentage of Failed or Deferred Messages a Domain May Send Per Hour (Continued) • Initial Default/Catch-All Forwarder Destination • PHP Configuration • Introduction • Configuration of the Password’s Strength • Enable Greylisting • Enable cPHulk • SMTP Restrictions • Exim Configuration Manager • Tweak Settings • Max Hourly Emails Per Domain

  3. Introduction • The aim of this PPT is to provide information on the best practices that need to be followed to ensure the prevention of email abuse on a cPanel & WHM server. cPanel & WHM is meant for automating tasks related to web hosting for Linux operating system. • The “Best Website Hosting Company”, the “Best Cloud Hosting Company”, the “Best Reseller Hosting Company”, etc., these are some of the terms that are used to refer to those hosting service providers that excel in providing hosting service. Hosting service is provided by web hosting companies and ensures that websites are always accessible and up and running without any issues.

  4. Configuration of the Password’s Strength • Increasing the minimum password strength with regard to the mail accounts of the users, results in a decrease in the risk of a hacker guessing the passwords correctly. The Password Strength Configuration interface of WHM needs to be used for defining the minimum password strength for the mail accounts of the users. It is recommended that the default minimum password strength be set to at least 50. WHM >> Home >> Security Center >> Password Strength Configuration

  5. Enable Greylisting • Enabling the service of Greylisting helps protect a server against spam or unwanted email. When this service has been enabled, any email from a sender that is unrecognized by the server, is temporarily rejected by the mail server. In the event that the email is legit, there are attempts to resend it by the originating server, after a delay. Once enough time has passed, the email is accepted by the server. • In order to enable this feature, you need to navigate to the Greylisting interface of WHM and then click Off to toggle the status of the feature. WHM >> Home >> Email >> Greylisting

  6. Enable cPHulk • Protection against brute force attacks for a server is ensured by cPHulk. Enabling cPHulk helps to reduce the chances of brute force attack being used by a hacker for gaining access to the mail accounts of a server. • You need to navigate to the CPHulk Brute Force Protection interface of WHM, for enabling this feature. Then you need to click Off in order to toggle the status of the feature. WHM >> Home >> Security Center >> CPHulk Brute Force Protection

  7. 1-800-123 -8156 Whoa! That’s a big number, aren’t you proud?

  8. SMTP Restrictions • Spammers cannot interact directly with the remote mail servers when SMTP Restrictions feature is enabled. Moreover, they cannot work around the settings for mail security either. You need to navigate to the SMTP Restrictions interface in WHM and click Enable in order to enable this feature. WHM >> Home >> Security Center >> SMTP Restrictions • The outgoing email connection attempts to the MTA (Mail Transfer Agent), the root user and to the mailman system user are restricted by this feature. Moreover, this feature makes sure that both scripts and users use the sendmail binary of Exim.

  9. SMTP Restrictions • Numerous options with regard to spam and abuse prevention are provided by the Exim Configuration Manager interface of WHM. WHM >> Home >> Service Configuration >> Exim Configuration Manager

  10. Tweak Settings • Certain settings that are present in the Mail section of the Tweak Settings interface in WHM, aid in preventing email abuse. These settings are mentioned in the following slides.

  11. Max Hourly Emails Per Domain This setting serves the purpose of specifying the maximum number of emails which can be sent by each domain in every hour. Its default setting is Unlimited. The following points need to be mentioned in this context: • Email send limits are enforced by the system only on remote email deliveries. • This setting will not appear if the Exim Mail Server service in the Service Manager interface of WHM is disabled. WHM >> Home >> Service Configuration >> Service Manager • This setting will not function if the Eximstats driver in the Service Manager interface of WHM is disabled. WHM >> Home >> Service Configuration >> Service Manager This setting doesn’t override the below-mentioned settings: • Maximum Hourly Email by Domain Relayed • Maximum percentage of failed or deferred messages a domain may send per hour It is recommended that such a value be specified that is not Unlimited in order to prevent email abuse.

  12. Max Hourly Emails Per Domain (Continued) • If the option for Max Hourly Emails Per Domain is set to 500, then each of the hosted domains can send 500 email messages in every hour. You can use the setting, the percentage of email messages (above the account’s hourly maximum) to queue and retry for delivery, for specifying a soft limit.

  13. Account-Specific Max Hourly Emails Per Domain Settings • When you want to specify values for an individual package or an individual account, you need to use the Edit a Package interface of WHM or the Modify an Account interface of WHM. WHM >> Home >> Packages >> Edit a Package • Or WHM >> Home >> Account Functions >> Modify an Account • You need to carry out the below-mentioned steps for manually editing the cpuser file, in order to enable this setting from the command line. • Open the file, /var/cpanel/users/username from the command line. In it, the term “username” represents the desired account username. • Add the MAX_EMAIL_PER_HOUR key in this file and specify the selected username’s value. • Run the script, /usr/local/cpanel/scripts/updateuserdomains

  14. Prevent “nobody” from Sending Mail • This setting makes sure that the nobody user is denied the ability to send mail to a remote address. The default setting is set to On. It is recommended that you select the On option to prevent email abuse. It is the PHP and CGI scripts, which usually run as the nobody user. You need to enable the suEXEC or mod_php modules in the Apache configuration in order to use a PHP or CGI script to send mail.

  15. The Percentage of Email Messages (above the Account's Hourly Maximum) to Queue and Retry for Delivery • It is specified by this setting if the outgoing messages for later delivery should be queued, once a domain reaches its limit with regard to outgoing messages per hour. This setting’s minimum value is 100 and its maximum value is 10,000. • The following key points need to be mentioned in this context: • This option needs to be set to 100 in order to force the failure of all outgoing messages, once the domain reaches its limit. • This setting will not appear if the Exim Mail Server service in the Service Manager interface of WHM is disabled. WHM >> Home >> Service Configuration >> Service Manager • This setting will not function if the Eximstats driver in the Service Manager interface of WHM is disabled. WHM >> Home >> Service Configuration >> Service Manager

  16. Maximum Percentage of Failed or Deferred Messages a Domain May Send Per Hour Through this setting the maximum percentage of failed or deferred messages, which might be sent by your domain in every hour, can be specified. The default for this setting is set to Unlimited. Outgoing mails from a domain are temporarily blocked by your server, when both of the below-mentioned conditions are true. • The number of failed or deferred messages sent by the domain equals that specified in the setting, Number of failed or deferred messages a domain may send before protections can be triggered. • In the total number of sent messages, the percentage of failed or deferred messages is equal to or greater than the percentage that has been specified. All outgoing and local mail, for the previous hour, are examined by the system for determining if these conditions are met. When only one of the above-mentioned conditions is true, outgoing mail isn’t blocked by the system.

  17. Maximum Percentage of Failed or Deferred Messages a Domain May Send Per Hour (Continued) • Maximum Percentage of Failed or Deferred Messages a Domain May Send Per Hour (Continued)

  18. Initial Default/Catch-All Forwarder Destination The initial forwarding destination with regard to the default/catch-all email addresses for new accounts is specified by this setting. Emails received by the non-existent users on a server’s domain are handled by the default address. It is recommended that this setting be changed from System account (default) to Fail, if a lot of spam is being received on the default accounts. The default setting for newly-created accounts is changed by this setting. The following steps need to be carried out for changing this setting for an existing account: • Log in to the specific cPanel account or navigate to the cPanel interface of the account through the List Accounts interface of WHM. WHM >> Home >> Account Information >> List Accounts • Navigate to the Default Address interface of cPanel. cPanel >> Home >> Email >> Default Address • Select from the menu, Send all unrouted email for the following domain, that domain for which you need to set a default address. • Select the option, Discard the email while your server processes it by SMTP time with an error message. This option sends an error message to the sender. • Enter an error message in the text box, Failure Message (seen by sender) • Click Change.

  19. PHP Configuration • Server security can be improved by configuring PHP and suEXEC, ModRuid2, or suPHP. Through this configuration you can have information regarding which users run which processes system-wide. It needs to be mentioned here that suEXEC should not be enabled with ModRuid2, as suEXEC isn’t compatible with it. • CGI applications are forced by ModRuid2 and suPHP to run as the cPanel account user. Moreover, some of the POSIX.1e capabilities are exploited by ModRuid2 in order to ensure performance enhancements over the default suEXEC configuration of Apache. CGI and PHP applications are forced by the suEXEC Apache module to run as the cPanel account user.

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