Subject: NotesLinks
are a special ‘object’ enbedded in a Notes RichText item.
The Notes mail router preserves them when sending Notes To Notes
but if you Send a Notes Mail to an internet address then
the tranmission format may not support all Notes features.
and a doclink is one that is usually lost.
If you are certain that the recipient is another Notes User,
then try setting the Item “mailFormat” to “E” (encapsulated)
on the mail.
You could do this as part of the action. Not sure how well this works n 6+
If your applications is Web enabled and on a suitable server
you could senda URL instead of a Link.
either a Notes: URL to launch the client
or a http URL to launch a browser.
If the recipient is NOT using Notes as their mail client
(but do have Notes installed for use as a groupware application)
you can send information equivalent to a link in the form of an attachment - to be specific an NDL file.
When a user opens this file from outlook say, Notes is launched at the correct document.
Once again You would have to create and attach the file in teh action that sends the mail. - and Lotus dont exactly proclaim the NDL format widely 
The downside of all these fixes is that you must do this in EVERY case.
If you need a centralised solution, there are 3rd party addins for the NotesMail router that automatically do this conversion for all emails wherever needed e.g.
Of course this costs cash money - however much time it saves
So the simplest solution remains, if sending FROM Notes TO notes, why not make use of teh superior features?
What is the advantage of using an internet address if the email finishes up in a Notes Inbox anyway?