If you’re looking for a quick and easy way to send email attachments there is no faster way than by using Mail.

We all know the standard way. Open Mail…Select New Message…click on
the Attachment Paper Clip icon…fill out your email…and Send.

There is actually a much quicker way to do this. Just take the
attachment you would like to send, and drag it to the Mail icon in the
Dock. Mail will launch, a new message will pop up, and your file will
already be attached.

Fill our your email, and click Send.

via Mactips.org