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| ShaoLin Aptus 2.0 Installation and Operations Guide | ||
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| Prev | Chapter 12. Tips on the Linux environment | Next |
The mailing system is also important in a Unix/Linux workstation environment. We will discuss 2 commonly used mailing system, Sendmail and qmail.
Sendmail is included almost in every Unix/Linux distributions, it uses the standard Unix mbox format. Where mbox format stores all messages in a single file linearly. With today's high demand email systems, it is not quite efficient to use this kind of mailbox format. If you are deleting the first message, it will required to shift the whole mailbox from the end to the beginning. This mailbox format is also not safe, if you are on the way operating your mailbox and having a system crash, you can loose the whole mailbox easily. It likely that large file is easier to get corrupted against small files. Sendmail also store user inbox in /var/spool/mail/[userid], the mailbox doesn't live in user home directories, it diverse the disk quota management and require additional work to backup those mailboxes other than just backing the system home directory where important user data files are located. Local mailboxes may not work correctly on Aptus clients because /var/spool/mail does not locate on a sharable file system. It is also unsafe to mount this spool folder using NFS. Therefore, it may require to use IMAP services on the mail server even in the local area network, resulted increasing the load of mail servers.
It is likely a centralized storage Linux/Unix network will have the server running IMAP, this will prevent users being downloading messages and deleting messages from their local storage. Having an IMAP server running over the mbox formated mailboxes can be very slow. Since IMAP server has to walk and search through a large file. Experience shows the memory consumption is very high on IMAP servers with mbox formated mailboxes. It is also confusing between folders, directories and files. Email clients usually refer mailboxes to folders, folders usually refer to directories in file systems, it may cause some email clients not to recognize sub folders correctly.
There is also a commercial version of Sendmail may perform better and has commercial support. For more information, please see the Sendmail official website.
Qmail is a proven scalable and fast mailing system for Unix/Linux. Large mailing systems like Hotmail used Qmail to setup their large scale mailing system. qmail use the maildir format to store messages. Where messages are stored in individual files. This will minimize the chance of having mailbox corruption. qmail can be easily configured to put all messages of users to put in their home directory, local mail can be easily retrieved from home directories without the need of using IMAP services. This will reduce load of mail servers tremendously. It is strongly suggested to use Qmail in a corporate environment where email traffics are usually heavy.
Qmail is also good for NFS delivery, that means you can have a stand alone separated operation mail server. This will allow you to setup a separate mail server and delivering mail to the home directory server directly without having to run qmail from your home directory server.
For more information, please see the Qmail official website.
