The Vacation Log is associated with the use of a Vacation Message. It lists people who have been trying to contact you in your absence (and also prevents duplicate messages being sent out). For example:-
2001-06-18 12:56:39 To: A. Person <someone@somewhere.com> Subject: Auto reply Re: another one 2001-06-25 14:24:04 previously sent to A. Person <someone@somewhere.com>
If you have a vacation message set up (or have had one and have not cleared the log) then the names of people to whom the auto-reply has been sent will be written to a log file. If there are entries in the log file then when you enter this screen it will look something like the screen above.
Each entry has the date and time the auto-reply was sent. The first entry for each person contains the name of the respondent and the subject of their mail. Subsequent entries for the same person note that the auto-reply has been previously sent (and hence has not been sent again).
Each time you set up a new vacation message you need to clear the existing log so that a copy of your new message can be sent to people who have previously received the old message. Selecting the Clear vacation log button does this.
If there are no entries in your log then the message
No vacation log at this time
is displayed in place of the list of names.