org-link-frame-setup

org-link-frame-setup is a variable defined in `org.el'.
Its value is

((vm . vm-visit-folder-other-frame)
 (vm-imap . vm-visit-imap-folder-other-frame)
 (gnus . org-gnus-no-new-news)
 (file . find-file-other-window)
 (wl . wl-other-frame))

Documentation:
Setup the frame configuration for following links.
When following a link with Emacs, it may often be useful to display
this link in another window or frame. This variable can be used to
set this up for the different types of links.
For VM, use any of
`vm-visit-folder'
`vm-visit-folder-other-window'
`vm-visit-folder-other-frame'
For Gnus, use any of
`gnus'
`gnus-other-frame'
`org-gnus-no-new-news'
For FILE, use any of
`find-file'
`find-file-other-window'
`find-file-other-frame'
For Wanderlust use any of
`wl'
`wl-other-frame'
For the calendar, use the variable `calendar-setup'.
For BBDB, it is currently only possible to display the matches in
another window.

You can customize this variable.