A mail server is software that can receive, send, cache, and forward messages and communications. The messages can be retrieved and processed by email clients. Mail servers act as mail transfer agents(MTAs) that forward the stored messages to the next mail server using Simple Mail Transfer Protocol( SMTP), up to the mail server that the receiving user has logged into with his or her e-mail address.
Users can access mail servers through their email account with the email address. The mail address includes the host address, often that of a provider, and the country code, the top level domain( TLD). E-mails sent from an e-mail client to an e-mail server are cached until they are picked up by the recipient. This is done using the Post Office Protocol( POP) or the Internet Message Access Protocol( IMAP). The e-mail client must log into its mail server using its e-mail account.
Logging into mail servers can usually be done with the user's preferred client, which does not require a special email client. Many mail servers offer client software that allows direct access through the web browser. For user authentication, many mail servers have their own databases with access data. Most mail servers support database access with Open Database Connectivity( ODBC), Lightweight Directory Access Protocol( LDAP) for access to Internet directory services, and Active Directory Service( ADS) and Secure Socket Layer ( SSL) for authentication.
An important aspect of mail servers is email security with protection from viruses, spam, and hackers. Mail servers have spam filters with which they identify spam and virus scanners with which they block virus-laden mail.