Version 76 Documentation
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(WHM >> Home  >> Service Configuration >> Mailserver Configuration)

This interface allow you to configure the POP3 and IMAP protocols that the Dovecot® mail servers use. The options in this document only appear when you access this interface while you run the Dovecot mail server.

Important:

Email authentication requires a valid cPanel license. If your license expires, mail delivery will continue to function. However, your mail client will not authenticate with the cPanel server. You must renew your cPanel license to reenable this service.


Mailserver Configuration options

Select the desired settings for each option in the table below, and then click Save Changes.

  • To return to the default values for all configuration options, click Use Default Values.
  • To undo your changes, click Reset Form. 
Configuration optionDescription
Protocols Enabled
Select the checkboxes to enable the desired protocols.

Notes:

  • You cannot disable Local Mail Transport Protocol (LMTP).
  • cPanel’s Webmail feature requires that you enable the Internet Message Access Protocol (IMAP) protocol.
IPv6 Enabled
Select the checkboxes to enable IPv6 address connection requests on the desired protocols.

Important:

You must select the desired protocols' Protocols Enabled checkboxes before you select those protocols' IPv6 Enabled checkboxes.

Allow Plaintext Authentication (from remote clients)

This setting allows remote email clients to authenticate without encryption. Select the desired option from the menu:

  • yes — Dovecot allows remote connections to authenticate without encryption.
  • no — Dovecot only allows connections that originated on the local server to authenticate without encryption. 

Note:

We recommend that you set this option to no if you wish to require remote webmail logins to use encryption.

SSL Cipher List
The list of ciphers, in standard format, that the mail server can use to connect to your server with the POP3 protocol.

For more information, read OpenSSL's ciphers documentation .

SSL ProtocolsThe list of SSL protocols that the mail server uses. Typically, you will only adjust this setting for PCI compliance.
Maximum Number of Mail ProcessesThe maximum number of mail processes that may run at one time.
Process Memory Limit for Mail (MB)

The maximum memory usage of the IMAP and POP3 processes, in Megabytes.

Because these processes mostly read memory-mapped files, high limits rarely affect server performance.

Maximum IMAP Connections Per IP Address
The maximum number of simultaneous IMAP connections that one IP address's mail server may make.

Note:

The system only applies this setting if you enabled an IMAP protocol. 

Interval between IMAP IDLE "OK Still here" messages

The number of minutes between IMAP IDLE "OK Still here" messages.

Note:

Increase this number in order to increase battery life for mobile clients.

Maximum POP3 Connections per IP Address
The maximum number of simultaneous POP3 connections that one IP address's mail server may make.

Note:

The system only applies this setting if you enabled the POP3 protocol. 

Number of Spare Authentication ProcessesThe number of spare authentication processes to run to listen for new connections.
Maximum Number of Authentication Processes
The maximum number of authentication daemons that can run simultaneously. Consider the needs of your mail server before you enter a value that is not the default value.

Notes:

  • A high number of authentication daemons can cause your server to run slowly. Authentication daemons can consume large amounts of system resources.
  • A low number of authentication daemons can cause your server to run slowly due to a lack of daemons to authenticate each session.
Process Memory Limit for Authentication (MB)The maximum amount of memory that the IMAP and POP3 authentication processes may use, in Megabytes.
Size of Authentication Cache (MB)

The maximum amount of space on the hard drive that the cache file may use, in Megabytes.

The cache file contains validated logins. This allows the mail server to retrieve mail multiple times before it must check login credentials again.

Note:

The value that you input cannot exceed four characters, which includes the required M character (for example, 100M ).

Time to Cache Successful Logins

The amount of time, in seconds, that the cache file stores a successful login attempt's record.

Note:

Lower this value to decrease the likelihood of problems when users update their passwords. 

Time to Cache Failed Logins

The amount of time, in seconds, that the cache file stores a failed login attempt's record.

Note:

Lower this value to decrease the likelihood of problems when users update their passwords. 

Use New Authentication Process for Each Connection

Whether the mail server uses a newly-created authentication process each time that a connection attempt occurs. Select yes to improve Dovecot security. 

Note:

Heavily-loaded servers may experience significant performance issues if you select yes.

Process Memory Limit: config (MB)

The maximum virtual memory size (VSZ) of Dovecot’s internal config service, in Megabytes. Each SSL/TLS certificate that Dovecot tracks requires additional memory. To ensure that Dovecot runs correctly, increase this value on servers with many domains.

This option defaults to 2048. We recommend that you set this value to at least 512.

Idle Check Interval

The amount of time, in seconds, between updates to idle IMAP connections.

Notes:

  • We recommend that you use the default setting (30 seconds).
  • Lower this value to cause idle clients to see new messages faster. 
  • Lower values may increase your server load slightly.
Include Trash in Quota

This option determines whether the system will count email messages in the Trash folder against the user's quota.

This option defaults to disabled.

Note:

After you modify this option, you must run the following command on the command line as the root user in order to recalculate existing quotas:

/usr/local/cpanel/scripts/generate_maildirsize --allaccounts --confirm
Compress Messages

This option allows the system to compress recently created and delivered messages.

This option defaults to disabled.

Compression Level

The compression level at which to save messages when you enable Compress Messages.

This option defaults to 6.

Auto Expunge Trash

Select this checkbox to allow the system to delete messages in the Trash folder based on the number of days that you configure in the Trash Expire Time option. 

This option defaults to disabled.

Note:

This option will only delete messages in the Trash folder that the account receives after you enable this option. For example, if you enable this option on April 1st, this option will not delete messages older than March 31st.

Trash Expire Time

The number of days that the mail server should keep messages in the Trash folder before the Auto Expunge Trash option deletes the messages. 

This option defaults to 30 days. 

Note:

This option only actives when you enable the Auto Expunge Trash option.

MDBOX rotation size (MB)

The maximum size of an MDBOX mailbox file, in Megabytes, before the system rotates it.

Enter a value that contains an integer value and the M character (for example, 100M). This value cannot exceed 999M and defaults to 2M.

Note:

The value that you enter cannot exceed four characters, which includes the required M character (for example, 100M ).

MDBOX rotation interval (Weeks or Days)

The maximum time that an MDBOX mailbox file may exist before the system rotates it.

For example, 2w represents a two week rotation interval.

Enter a value that consists of an integer and the letter w, which represents weeks, or the letter d, which represents days.

This option defaults to 0, which disables time-based rotation of the MDBOX mailbox files.

Disk Quota Delivery Failure Response

This option determines how Dovecot will handle delivery to a mailbox that reaches its mailbox quota or to a cPanel account that reaches its system disk quota.

  • Reject the message permanently. — This setting rejects the message and returns it to the sender.
  • Defer delivery temporarily. — This setting allows the user to free disk space or increase disk quota before the system attempts to deliver the message again.
Minimum Available LMTP Processes

This option determines the minimum number of processes for the system to reserve in order to accept client connections.

This option defaults to 0, which configures the LMTP server to only start when the system needs it, and needs to conserve memory.

LMTP Process Limit

This option determines the maximum number of processes that the system will allow the LMTP server to run.

This option defaults to 500.

This option limits the maximum number of concurrent LMTP deliveries per user. A value of 0 disables the per-user limit.

This option defaults to 4.

Add Dovecot options

You can also add options that do  not  exist in the  Configure Dovecot  interface to configure the Dovecot mail server. To do this, select the tab that corresponds to the Dovecot template that you wish to modify.

To modify the template for the /etc/dovecot/dovecot.conf file, perform the following steps:

  1. Copy the /var/cpanel/templates/dovecot2.2/main.default file to the /var/cpanel/templates/dovecot2.2/main.local file.

  2. Open the /var/cpanel/templates/dovecot2.2/main.local file with a text editor and edit the files to reflect your desired settings, for example:

    login_trusted_networks: 192.168.1.0/24


    Note:

    This example automatically creates the mail.domain.com domain for all domains that use the Mail SNI option in WHM's Manage SSL Hosts interface (WHM >> Home >> SSL/TLS >> Manage SSL Hosts).

  3. Save your changes to the file.

  4. Rebuild the Dovecot mail server to apply the new configuration settings. To do this, run the following script:

    /usr/local/cpanel/scripts/builddovecotconf
  5. Restart the Dovecot mail server. To do this, run the /scripts/restartsrv_dovecot command.

To modify the template for the /etc/dovecot/sni.conf file, perform the following steps:

  1. Copy the /var/cpanel/templates/dovecotSNI/main.default file to the /var/cpanel/templates/dovecotSNI/main.local file.

  2. Open the /var/cpanel/templates/dovecotSNI/main.local  file with a text editor and e dit the files to reflect your desired settings. For example:

    [% FOREACH domain IN mail_sni_domains.sort -%]

local_name [% domain %] {
    ssl_cert = <[% mail_sni_domains.$domain.crt %]
    ssl_key = <[% mail_sni_domains.$domain.key %]
    [%- IF mail_sni_domains.$domain.cabundle %]
    ssl_ca = <[% mail_sni_domains.$domain.cabundle %]
    [%- END %]
}

local_name mail.[% domain %] {
    ssl_cert = <[% mail_sni_domains.$domain.crt %]
    ssl_key = <[% mail_sni_domains.$domain.key %]
    [%- IF mail_sni_domains.$domain.cabundle %]
    ssl_ca = <[% mail_sni_domains.$domain.cabundle %]
    [%- END %]
}


    Note:

    This example automatically creates the mail.domain.com domain for all domains that use the Mail SNI option in WHM's Manage SSL Hosts interface (WHM >> Home >> SSL/TLS >> Manage SSL Hosts).

  3. Save your changes to the file.

  4. Rebuild the Dovecot mail server to apply the new configuration settings. To do this, run the following script:

    /usr/local/cpanel/scripts/builddovecotconf
  5. Restart the Dovecot mail server. To do this, run the /scripts/restartsrv_dovecot command.

Additional documentation

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