Jeff Richards describes how to do it in this post:
Basically, your Email template needs to have the following text:
#recordanchor# <Anchor text goes here> #recordanchorend#
If you’re manually constructing the link (e.g. via a script), you can use the same “SessionFind” URL structure e.g.:
The above URL will redirect the user to the Company Summary page (Act=200) for the company (key0=1) with a comp_companyid of ‘300123’ (key1=300123).
NOTE: The user will always have to login when clicking these links (even if they already have an open session).