Maildirsize

maildirsize is a file used in the Maildir email storage format to store the total size of all messages in a Maildir directory.

In a Maildir directory, each email message is stored in a separate file, and the file name follows a specific format, such as 12345.new, 12345.cur, or 12345.siz. The 12345 part is a unique identifier for the message.

The maildirsize file is a special file that contains a list of the total size of all messages in the directory, in bytes. The file is typically stored in the same directory as the email messages, and its name is maildirsize.

The format of the maildirsize file is a series of lines, each representing the total size of a specific message. Each line contains the message ID (the same as the file name without the extension) followed by the total size of the message in bytes.

For example, the maildirsize file might contain the following lines:

12345 1234
12346 5678
12347 9012

This indicates that the message with ID 12345 has a total size of 1234 bytes, the message with ID 12346 has a total size of 5678 bytes, and so on.

The maildirsize file is used by email clients and servers to quickly determine the total size of all messages in a Maildir directory, without having to scan the entire directory. This can be useful for tasks such as calculating the total size of a user's email account or determining the available disk space.

It's worth noting that the maildirsize file is not required for the Maildir format to function, but it can be useful for improving performance and reducing the amount of disk space used by the email storage.