How does Eudora work with a POP server?

What does it do, what problems can occur?

Let's consider the fictional Ada Byron, whose netid is adabyron and whose account is on tigger.

1. When Ada's Eudora attaches to the POP server on tigger, it "puts a lock" on her email Inbox: /usr/mail/adabyron
   
   The lock is to keep the Inbox from being changed while the POP server is working with it.
   
   
2. The POP server then copies /usr/mail/adabyron to the file: /usr/mail/.adabyron.pop
   
   Both /usr/mail/adabyron and /usr/mail/.adabyron.pop are readable and writable directly by their owner, Ada Byron, although it's generally not a good idea to write to them with anything besides an email program since their format is rather delicate.
   
   
3. After the POP server finishes copying the Inbox file, it erases the messages it moved to the .pop file, leaving the Inbox (/usr/mail/adabyron) empty. Then the POP server removes the file lock, opening Ada's Inbox for new incoming email messages.
   
   Copying the file from one location on the server machine to another is fast, so making a copy of the file on the server before allowing the new incoming email to be downloaded to your personal computer limits the time that the POP server has to maintain a "lock" on your Inbox, making it far less likely to get in the way of new incoming messages.
   
   
4. The POP server then locks the .adabyron.pop file, and looks at it to see which messages it should download and which ones it's already seen. It keeps a lock on the file during the download.

Problems occur if the download is interrupted for whatever reason. First, it leaves that the file being worked on locked, as the process that locked it hasn't been terminated. Second, it leaves all the mail in the .adabyron.pop file, and leaves your Inbox/usr/mail/.adabyron.pop empty.

Usually, Eudora (or whatever email program) can recover from this -- you can just reconnect and the POP server will finish up and clean up. But not always. Sometimes Eudora will connect and say that it can't do anything because its "maildrop is locked", or it doesn't find the mail that you know is there. You can fix this and other problems from the ACCC Email Tools page.