Shell Programming and Scripting

I'm working on implementing a mail indexer and it currently saves every file with a series of numbers with no extension. ex. 021545545544

I was wondering if someone could point me in the correct direction for a script that would check all the files and give it a .eml extension if it doesn't already have one.

Code:

find /home/administrator/Maildir/test -type f -exec mv '{}' '{}'.eml \;

So far this is what I have but id like it to not add the eml extension if it already has one.

Code:

find /home/administrator/Maildir/test -type f ! -name '*.eml' -exec mv '{}' '{}'.eml \;