When sending to your External Access Database Group if you get a message “Unable to determine size of Group” you should do the following :

Create a Query in your Access database that returns the appropriate records/fields from the Access tables.  In GroupMail when creating the Group use the SQL “Select * from Query”, this will result in the recipient count being displayed in GroupMail.  [To modify an existing Group, simply go to Groups, right click on the Group and go to Modify].

Do not use the “ORDER BY” cluase in your SQL statement or you will get an error.