Gmail Update: You Can Now Select Multiple Attachments
2009 February 26
The ability to select multiple file attachments simultaneously when attaching files to Gmail messages was recently implemented by Google.
If you’re using Windows and want to add more than one file attachment, hold down the Ctrl key while selecting each file.
If you’re using a Mac, hold down the Cmd (Apple) key.
You’ll also see a nifty progress bar while the attachment(s) load(s).