Emails are delivered extremely fast when compared to traditional post.
Emails can be sent 24 hours a day, 365 days a year.
Webmail means emails can be sent and received from any computer, anywhere in the world, that has an internet connection.
Cheap - when using broadband, each email sent is effectively free. Dial-up users are charged at local call rates but it only takes a few seconds (for conventional email, eg text only) to send an email.
Emails can be sent to one person or several people.
The recipient needs access to the internet to receive email.
Viruses are easily spread via email attachments (most email providers scan emails for viruses on your behalf).
Phishing - sending an email to a user falsely claiming to be a legitimate company to scam the user into providing information, such as personal information and bank account numbers on a bogus website. The details will then be used for identity theft.
No guarantee the mail will be read until the user logs on and checks their email.