Below are results from testing Exchange2010 Sharepoint2010 integration for in-coming email enabled lists in SharePoint. It covers several questions a customer of mine recently asked me about how display names look in the GAL as well as possible scenarios in which a duplicate email name is entered when email enabling a list.
It covers the following   

Auto created contact in AD 


The "Automatically update email addresses based on email address policy" setting must be checked/enabled
on SP mail contact in order for it to appear in GAL


The name will then appear in the GAL in the format of site name



Now what happens when trying to assign the same email name (  to a different list in SharePoint  So in this scenario we have http://webapp1/sites/teamsite/list1 (where list1 has email name = list1) http://webapp2/sites/teamsite/list1
The follow error will occur if we try to set email name on  http://webapp2/sites/teamsite/list1  to" list1" which prevents duplicate emails names from being created

However if I give I give the second List1 list unique email name like "list2" it will be created successfully



 So in this scenario we now have
http://webapp1/sites/teamsite/list1  (where list1 has email name = list1)
http://webapp2/sites/teamsite/list1  (where list1 has email name = list2)

 We end up with duplicate entries in the GAL as below


This is because the display name is created/concatenated from the site name and list name as shown below