preserve access time with GNU tar

[Sven Rudolph]

When I save the mail folders (/var/mail/*) with GNU tar the access
time is set.

This makes xbiff believe that the mail was read, so it changes back to
the "unflagged mailbox" picture.

I guess that GNU tar's --atime-preserve avoids this. Right? (But this
makes differential backup of these files impossible?)

How can I pass this option to GNU tar for the /var/mail disk?

        Sven