BK.ru is a Russian e-mail service provider, which provides a series of functions, including registering, logging in, managing contacts, setting e-mail signatures, using e-mail filters and protecting account security. BK.ru mailbox has become one of the most popular mailboxes in Russia because of its unique usage and long history. Mailbox generally refers to the trusted equipment set up by postal institutions in post offices, roadsides or public places to accept mail delivered by the public, especially public mailboxes. In modern network communication, mailbox usually refers to email account, which is a network service for sending and receiving emails. Different from the traditional mail service, mailbox has the advantages of easy management and storage, cross-device sharing, real-time transmission and support for multiple formats. With the popularity of mobile Internet and smart phones, people rely more and more on mailboxes for daily work and life communication. At the same time, with the development of big data, cloud computing and artificial intelligence technology, the mailbox has also been given more intelligent functions, such as intelligent recommendation and security protection.