The structure of the e-mail service

E-mail appeared in 1971 and is still one of the main means of communication. An address has two parts: the mailbox name and the domain, separated by the @ sign (bahor2026@example.uz). The message header has the fields From, To, Cc (copy), Bcc (hidden copy – the other recipients do not see it) and Subject, followed by the text and attachments. The path of a message: you write it in a mail program (or in a browser) – this is the MUA. It sends the message to a server with SMTP; these servers (MTA) pass it along a chain. The server of the recipient's domain is found through the MX record in DNS. The last server puts the message into the mailbox with the help of the MDA; the recipient reads it with IMAP or POP3 (or in a browser). Modern services encrypt the connection with TLS. Attachments are encoded with base64 so that they can be sent as text, so the size grows by about 4/3 (33%): 3 bytes become 4 characters. So with a limit of 25 MB the real file can be only about 18 MB. The mailbox storage is on the server disk and does not take the computer's memory (for example, free Gmail shares its 15 GB with other Google services). E-mail safety: (1) switch on two-step verification and use a separate long password for each service; (2) do not open attachments and links in a message from an unknown sender, especially .exe, .scr or macro documents; (3) signs of phishing: rushing (“your account will be closed in 24 hours”), asking for a password or code, a sender address that looks like an official one but is different, spelling mistakes; banks and state offices do not ask for passwords by e-mail; (4) spam is unwanted bulk mail: do not reply, do not trust the “unsubscribe” link in a distrusted message, and mark it as “spam”; (5) when writing to many people use Bcc and do not press “reply all” needlessly. E-mail etiquette: a clear subject, a greeting, a short and polite text, a signature; do not forward someone's message without permission. When registering, enter only the necessary personal data and add a second address or number for recovery.