Reply from the ToolBar
Sparrow’s Toolbar allows you to make all kind or reply and to forward mails.
To Forward or Reply All, just perform a long click on the Reply icon. A contextual menu will let you ‘Forward’ or ‘Reply All’ the selected mail.
To Reply All, you can also ⇧-⌘-R
To forward a mail, you can ⇧-⌘-F