INSERT trigger not SELECTing rows
I think you will have better luck pulling from inserted instead of from the base table (and of course fixing the typo that should have prevented compilation), but you should also consider not using e-mail from a trigger at all.

ALTER TRIGGER [dbo].[SendEmail_INS]
ON [dbo].[tbl_UNIT_INS]
FOR INSERT -- AFTER INSERT is the exact same thing as FOR INSERT.
AS
BEGIN
  EXEC msdb.dbo.sp_send_dbmail
     @query_result_header = 0,
     @exclude_query_output = 1,
     @profile_name = 'Outbound',
     @recipients = 'me@email.com', -- fixed missing quote here
     @query = N'SELECT * FROM inserted;',
     @subject = 'New Item Inserted';
END
GO