Mutt was originally designed as a [[w:Mail User Agent|Mail User Agent]] (MUA) and relied on locally accessible mailbox and [[w:sendmail|sendmail]] infrastructure. According to the Mutt homepage "though written from scratch, Mutt's initial interface was based largely on the [[w:Elm (email client)|ELM mail client]]". New to Mutt were message scoring and threading capabilities. Support for fetching and sending email via various protocols such as [[w:POP3|POP3]], [[w:IMAP|IMAP ]] and [[w:Simple Mail Transfer Protocol|SMTP]] was added later. Mutt relies on external tools for composing and filtering messages.