Forwarding emails and file attachments results in copies made of the copyright material and you can do so with the consent of the copyright owners. The consent of copyright owners can be express or implied. For example, some emails expressly invite you to forward them to your contacts who you think may be interested (e.g. publicity on a product launch). Other emails, by their nature (e.g. where social awareness or public education is involved), may imply that forwarding is allowed. When in doubt, you should check with the source.