A lot of email programs and providers have extra email add-ons. Signatures and attachments can get tricky, here's the scoop!
Many programs have a way to include an automatic signature that includes your name, company, address, email, phone number...any amount of additional contact info you might like to include. This is a good idea in case someone wants to get in touch with you in another way. If you can't set one up to post automatically, think about manually adding this to emails.
If you send an email with an attachment, be sure its an attachment they can open. You would hate to send over important information that can't be opened. Likewise, if you receive an attachment, only open it if you know the sender. Sometimes viruses can be stored in attachments.