IMAP: advanced account configuration

This article was written for Thunderbird but also applies to the Mozilla Suite. The main difference for the Mozilla Suite is that it uses a different menu to get to the account management settings

• Tools -> Account settings -> Server settings -> Advanced -> IMAP -> "maximum number of server connections to cache" defaults to 5. Courier IMAP servers default to 4 connections per TCP-IP address. This mismatch can cause apparent hangs, data loss, and messages to be downloaded instead of just headers. If you have one Courier account you need to lower the Thunderbird setting to 4 or less. If you have two Courier accounts you need to lower the setting in each account to 2 since its 4 connections per TCP-IP address, not per account. If you don't know whether you have a Courier IMAP server it doesn't hurt anything to lower the values.

• Thunderbird defaults to only showing subscribed folders. Thats a way to manage the clutter when you have a lot of remote folders and you don't want to see all of them in the folder pane. You subscribe a folder by right clicking on the remote inbox, selecting subscribe, expanding the inbox tree in the window, and subscribing whatever folders you want. You can configure it to show all folders by unchecking the checkmark at Tools -> Account settings ->Server settings -> Advanced -> IMAP -> "show only subscribed folders".

• If you have problems creating (or seeing) remote child folders you might be using a IMAP server that doesn't support both messages and child folders within a child folder. Try unchecking Tools -> Account settings ->Server settings -> Advanced -> IMAP -> "server supports folders that contain subfolders and messages" and use webmail to move the messages out of that child folder.

• The IDLE command is a extension to the IMAP protocol that lets the IMAP server notify Thunderbird when there is new mail by sending a command over the existing TCP-IP connection. If your IMAP server supports that you don't have to manually check for new mail or have Thunderbird poll for new mail every x minutes.

• Its usually best to leave the IMAP server directory field empty, check the checkmark for "allow server to overide these namespaces" and to use "INBOX." (the trailing period is critical) in the personal namespace field. There are some IMAP configurations where thats inappropiate but its not as common as most people think. If the namespace is not configured correctly you will typically see multiple copies of a child folder, child folders as peers to the inbox, or be unable to create child folders. Thunderbird normally displays the inbox folder as the root, with no peers.

• You can configure Thunderbird to automaticly check any or all remote folders for new mail.

• An IMAP account normally only downloads headers to the hard disk when checking for new mail. Your account would have a "inbox.msf" file but no "inbox." file. When you read a message it is fetched from the server unless its already cached in memory. If you want to maintain a local synched copy of a remote folder use Tools -> Account Settings -> Offline & Disk space -> Offline -> "select folders for offline use". That will store/update a copy of the selected remote folder as a mbox file, which you can only see when working offline.

• There are some advanced IMAP preferences that can be used to control whether an attachment is fetched if you don't open it, tweak how it fetches messages in chunks, how many deleted messages need to accumulate in a folder before the client issues an EXPUNGE command to permanently remove them etc.

• There are also some IMAP-specific preferences to automate compacting the inbox and emptying the trash on exit. It is perfectly appropiate for a message deleted in Thunderbird to be visible in webmail. Deleting a message just sets a flag, and its up to the GUI what it should do when there is a message with that flag set. However, once Thunderbird compacts (purges) that folder, the deleted message shouldn't be visible anymore from webmail because it has now been physically deleted.

• You can drag and drop a remote folder to a POP account or local folders, but not vice versa. You need to create the destination folder beforehand when uploading messages. This is a limitation of Thunderbird, not IMAP. Pegasus doens't have this limitation.

• Many IMAP servers default to a Sent Items folder, not a Sent folder. Thunderbird defaults to 'Sent' in Tools -> Account Setttings -> Copies & Folders -> When sending messages automaticly". Thunderbird will not create the folder if it doesn't exist.

• Its possible to change the remote trash folder. If you wanted to use a remote "Papierkorb" folder, find what server number is used for that account. You can normally figure this out by looking for the preference that specifies the host name. user_pref("mail.server.server1.name", "fastmail"); shows that my fastmail IMAP account uses server1. So I would add user_pref("mail.server.server1.trash_folder_name", "Papierkorb"); to prefs.js, start Thunderbird (you now have two trash folders), and then delete the old trash folder using webmail. If you wanted to use 'Gelöscht' (german for Trash) you would have to use user_pref("mail.server.server1.trash_folder_name", "Gel&APY-scht"); since the german Umlaute has to be encoded differently.