The Biff client is a new-mail notifier. It provides a button on your tkgoodstuff panel that can display an icon indicating the presence of new mail, a text message indicating "No Mail"/"New Mail", or both (optionally, "New Mail" is replaced by a counter of new messages).
Biff watches one or more "mailboxes": mail files, MH folders, or mailboxes on remote IMAP servers. For each mailbox, at a set interval Biff looks for unread messages in the mailbox and flags the presence of new mail by beeping and changing the icon and label of the Biff button. Each mailbox is assigned an "alert level", and the new-mail icon indicates the maximum alert-level of all mailboxes with new mail.
If you configure Biff to watch just one mailbox, it will display on the Biff button the number of new messages in it, if any, and mouse button 3 fetches a list of the messages. If you use multiple mailboxes, then mouse button 3 produces a menu that indicates how many new messages are in each mailbox, and which allows you to fetch a list of the messages in any of them. You can click on a message in the message list to view the message in full. If you like, Biff can also post a list of new messages in a mailbox when they arrive.
Clicking mouse button 1 on the Biff button launches your mailer program (the button stays depressed and inoperative until you exit the mailer program). Button 2 instructs Biff to regard as old mail any current new mail (displaying a no-mail icon and/or the label "No Mail"), and to wait until you get yet more mail before notifying you.
For each mailbox, you can choose (in the preferences manager) between several "methods" of testing for new mail: there are special methods for mailboxes on IMAP servers and for MH mailboxes (you don't know if your mailbox is MH-style? then it's almost certainly not), and three methods for detecting new mail in standard mail files (including spool files, such as the default mailbox /usr/spool/mail/username): "atime", "filesize", and "internal". With the method "atime" (the default), Biff decides that there's new mail when the file has been modified when or after it has last been accessed (its mtime is no less than its atime). With the method "filesize", Biff decides that there's new mail when the file is nonempty. The "internal" method scans the message headers for "Status:" lines, and treats messages with a status of "N" or with no "Status:" line as new. The "atime" or "internal" method is probably best for those who keep old mail in their spool file. The "filesize" method is better for those who normally regard all mail in the spool file as new mail.
The MH method is only for those using MH mailboxes AND automatic incorporation of new mail (e.g., by slocal or procmail), and is automatically used if the folder to be checked starts with a "+". With the mh method, we assume a message is new if it is in the "u" sequence in the .mh_sequences file in the folder or if its atime isn't after its mtime. NOTE: for automatic incorporation of new mail into MH folders, you must pipe messages (using slocal or procmail or deliver) into the MH program rcvstore, so that the MH unseen sequence is correctly updated. An example from my .procmailrc:
MHLIB=/usr/lib/mh :0 * ^(To|Cc|Subject):.*tkgoodstuff.* |$MHLIB/rcvstore +tkg
The IMAP method is for mailboxes on remote IMAP servers. You need to supply the mailbox name and your user name (at the server). Note: if you are unsure about the mailbox name, very likely your mailbox at the server is called "INBOX". You can supply your password (at the server) in the preferences manager, in which case it will be stored in your .tkgrc file (which it's up to you to protect!!), or you can leave your password blank in the preferences manager, in which case tkgoodstuff will ask you for it when the mailbox is first accessed.
All parameters are adjustable in the preferences manager.
Thanks to G. Dezern.