Messages can also be forwarded to somebody by clicking the Forward button in the toolbar. The compose screen will contain the message text and all attachments already added. You can still add more attachments or remove some you don’t want to forward.

The Forward toolbar button offers the following options:

Forward inline
In this (default) mode, the content of the original message is copied to the message text editor and can be altered or deleted. Also attachments of the original message are copied to the new message and can be removed individually. Attention: this mode can truncate or re-format HTML formatted messages.
Forward as attachment
With this option, the original message is copied as attachment to the forwarding message. This will preserve the message with all its formatting and attachments and doesn’t allow you to alter anything.