An e-mail system works with local, regional and global networks. It provides each subscriber with a centrally managed mailbox with its own e-mail address, to which only the respective subscriber has access via his e-mail account. The system accepts messages for each e-mail client under its e-mail address and keeps them ready for viewing by the person concerned. The participant can retrieve the messages by means of access authorization, change them, delete them or forward them to other recipients and download the attachments.
Messages are transferred from the sender to the destination computer, which manages the mailbox, via one or more intermediate computers called mail transfer agents(MTAs). E-mail communication is based on various e-mail protocols. These include the Simple Mail Transfer Protocol( SMTP) for sending e-mail, the Post Office Protocol( POP) and the Internet Message Access Protocol( IMAP) for receiving messages. Another e-mail protocol is Domain-based Message Authentication, Reporting and Conformance (DMARC). It is used for authentication and protects private individuals and companies from misuse of their e-mail addresses.
In connection with the Internet, all service providers( SP) offer e-mail accounts as a service. The most important standard for e-mail is the ITU recommendationX.400 for interpersonal messaging systems. Another important e-mail protocol is the Application Control Access Protocol( ACAP).