You should never create or rely on a DL that large.
Are these entries you entered only into the DL instead of your Contacts?
That's also not recommended.
You should look into a more reliable way to group Contacts, like Categories
or separate Contact subfolders.
To put these entries into a Contacts folder, you'd need to save the list as
a text file, clean it up, and save it a CSV file, then import it.