Before you run the PMDF Mailbox Servers configuration utility, you must install PMDF-MTA on your system. It is recommended that you also configure PMDF, as well as the PMDF Service Dispatcher, before you configure the PMDF POP and IMAP mailbox servers. (See Chapters 1, 2, and 3 if you have not already installed and configured PMDF-MTA. See Chapters 5 and 6 if you have not already configured the PMDF Service Dispatcher.

If you were previously using non-PMDF servers, you will need to shut down the old servers before you can use PMDF's multithreaded servers.

The PMDF POP and IMAP mailbox servers configuration utility prompts you for several pieces of information, including which POP and/or IMAP servers you want to run, as well as the number of simultaneous POP and IMAP connections you want to allow at your site. You will need to provide site-appropriate answers. For some of the questions, the configuration utility provides reasonable default values. You might want to take the default answers the first time you configure, and then later, after observing the actual POP and IMAP usage at your site, reconfigure with values that are appropriate for your site.

Configuration questions include the following:

• Whether you want to run the legacy mailbox IMAP server, or the MessageStore mailbox IMAP server, or neither server.
• Whether you want to run the legacy mailbox POP server, or the MessageStore mailbox POP server, or neither server.
• Whether you want to log IMAP and POP connections.
• Whether you want to run a POPPASSD server to support changing passwords from POP clients who are using the adhoc password changing mechanism (for example, Eudora).

  Note The POPPASSD protocol involves sending both the old and the new password "in the clear." Consider this point carefully when you are deciding whether or not to provide this service.

• Whether you want to enable PMDF's password changing web CGI.

If you choose to run a MessageStore IMAP or POP server, the utility will also configure the PMDF MessageStore and PMDF popstore for you. Therefore, you will be asked some additional questions, including:

• The pseudo domain name assigned to the MessageStore. This is the domain name which will be used to address mail to PMDF MessageStore users. For instance, if you want MessageStore users to have addresses in the form user@msgstore.example.com, you would use the domain name msgstore.example.com for the MessageStore.
• The local postmaster address.
• The default primary message storage quota to allow each user. The default account is granted this quota. When you create user accounts, they will be given this primary quota, unless you specify a different quota. A primary quota value of 0 means unlimited storage quota.
• The default overdraft message storage quota to allow each user. This is the amount that users are allowed to exceed their primary quota.¹ The default account is granted this overdraft quota, which is then used as a default setting for user accounts that you create.
• The number of days to retain PMDF popstore unread messages. If a user has not either downloaded or deleted a message after this limit, the message will either be deleted silently, or returned to its originator as unread. If you want to retain messages indefinitely, specify an age limit of 0.
• A special account name for posting to public folders in the MessageStore.

If you choose to run an IMAP server, you will be asked some additional questions, including:

• The maximum number of simultaneous IMAP connections you want to support on your system.

  Note This is not the total number of users, or even the total number of IMAP users. Rather, it is the maximum number of simultaneous IMAP connections. Some IMAP clients make (and keep open) more than one connection to the server. So the number of simultaneous IMAP connections can be higher than the number of simultaneous IMAP users. Unlike POP connections, IMAP connections tend to be long lasting---the IMAP client connects and stays connected as the IMAP user reads and moves messages between folders. Choose a number that provides reasonable access for your users, without overburdening your system resources.

• The maximum number of connections you want to allow per server process. To support a given number of simultaneous connections, there is a tradeoff between the number of processes used, and the number of connections handled per process. Fewer connections per process tend to result in greater responsiveness for the individual connections. However, the resulting need for more processes incurs greater system overhead. It is recommended that you choose a moderate number of connections per process.
• How often to check for new mail. (The legacy mailbox IMAP server continually checks for the new mail. This checking incurs overhead.)

If you choose to run a POP server, you will be asked some additional questions, including:

• The maximum number of simultaneous POP connections you want to support on your system.

  Note This is not the total number of users, or even the total number of POP users. Rather, it is the maximum number of POP users who will be connecting simultaneously. POP connections are usually brief---the POP client connects, downloads messages, and disconnects. Choose a number that provides reasonable access for your users, without overburdening your system resources.

• The maximum number of connections you want to allow per server process. To support a given number of simultaneous connections, there is a tradeoff between the number of processes used, and the number of connections handled per process. Fewer connections per process tend to result in greater responsiveness for the individual connections. However, the resulting need for more processes incurs greater system overhead. Process Software recommends you choose a moderate number of connections per process.
• Whether you want the server to support the POP3 UIDL command.
  The UIDL command lets POP clients use an identifier to keep track of messages. POP users who enable "leave mail on server" behavior typically appreciate having UIDL supported, as this lets their client keep track of which messages in their inbox have actually been read. Sites that want to discourage "leave mail on server" behavior should disable UIDL support.
• For the legacy mailbox POP server (POP access to the VMS MAIL mailbox), whether you want messages read via POP to be moved to the MAIL folder automatically. Note that POP clients can only access the NEWMAIL folder. So if a message gets moved to the MAIL folder, the POP client can no longer access it. But leaving read messages in the NEWMAIL folder causes the NEWMAIL folder to bloat, and causes the POP server to perform more work.
• For the legacy mailbox POP server (POP access to the VMS MAIL mailbox), whether the server should estimate the size of messages rather than determining their exact sizes. Such estimation allows the server to respond much more quickly in the case of users who have a lot of messages in the NEWMAIL folder, as the server does not have to read all of the messages to determinate their exact sizes.