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For cPanel & WHM version 64

(Home >> Email >> Mailbox Conversion)


This interface allows you to convert the format of cPanel accounts' mailboxes.

The maildir format uses flat files, which cause systems with large mail archives to exhaust their inode resources quickly.

The mdbox format stores multiple messages in a file and uses a simpler indexing scheme. This format requires fewer files, reduces inode usage significantly, and decreases disk space usage.


  • Unlike the maildir format, the mdbox format does not support symlinks.
    • For example, when a cPanel account owner uses Webmail on an account that uses the maildir format, the system displays every mailbox of the account's email users. However, on a cPanel account that uses the mdbox format, the system only displays the cPanel account's mailbox. The system does not display the mailboxes of the account's other email users.
    • For more information about symlinks in Dovecot, read Dovecot's Symlinks documentation.
  • When you convert from one mailbox format to another, the unique identifier (UID) for each email message on the server will change. The system uses UIDs to identify each message that a POP email account receives. Email clients that do not delete mail from the server use these UIDs to determine which messages to download. Due to this change in UIDs, mailbox conversions can cause POP email users to receive previously-downloaded messages as though they were new.

Convert mailboxes

The interface displays a summary of the accounts that use the mdbox and maildir formats. It also lists benefits and limitations for each format.

To convert an account's mailboxes from one format to the other, perform the following steps:

  1. Select the format to which to convert mailboxes and click Next.



  2. Select the checkboxes for the account or accounts to convert click Next.
    • Use the navigation tools at the top of the table to search for and select accounts.
    • To return to the previous step in the procedure, click Previous.
  3. Click Convert to convert the mailboxes for the selected account or accounts.

    • To convert the mailboxes and keep the files for the old format, select Keep old mailbox files.

    • To return to the previous step in the procedure, click Previous.

After you click Convert, the interface displays the status and progress of the conversion of mailboxes, and any warnings.

When you convert the mailboxes, the system creates the /storage directory in each account's /home/user/mail and /home/user/mail/domain/emailaccount directory. This directory contains all of the account's email messages that existed before you converted the mailbox's format.




Do not delete the /storage directory. Additionally, if you convert an account's mailboxes from the maildir format to the mdbox format, do not delete the   /mailboxes directory. The system requires that these directories remain for the mailboxes to function correctly.

Create disk space

The amount of mail that resides in the /storage directory does not count against the cPanel account's email account quota. However, this amount of mail does count against the cPanel account's disk space quota.

The mdbox format

To create disk space after you convert your mailboxes to the mdbox format, delete the following files:


The maildir format

To create disk space after you convert your mailboxes to the maildir format, delete the /mailboxes directory.

Additional documentation