Relay mail server

A relay mail server is a mail server that acts as a middleman between a mail client (such as a mail user agent) and a destination mail server. Its primary function is to forward email messages from the client to the destination server.

Here's how it works:

  1. A mail client (e.g., a webmail interface or a mail client software) sends an email message to the relay mail server.
  2. The relay mail server receives the email message and checks its configuration to determine whether to forward the message to a destination mail server or to store it locally.
  3. If the relay mail server is configured to forward the message, it connects to the destination mail server and sends the email message to it.
  4. The destination mail server receives the email message and stores it in the recipient's mailbox or delivers it to the recipient's email client.

Relay mail servers can be used for various purposes, such as:

  1. Email filtering: Relay mail servers can be configured to filter out spam, viruses, and other unwanted emails before forwarding them to the destination mail server.
  2. Email encryption: Relay mail servers can be used to encrypt email messages before forwarding them to the destination mail server, ensuring that the email content remains confidential.
  3. Email routing: Relay mail servers can be used to route email messages to different destination mail servers based on specific criteria, such as the recipient's email address or the sender's IP address.
  4. Load balancing: Relay mail servers can be used to distribute email traffic across multiple destination mail servers, improving the overall performance and reliability of the email system.

Types of relay mail servers:

  1. SMTP relay: An SMTP relay server is a specialized mail server that forwards email messages using the Simple Mail Transfer Protocol (SMTP).
  2. Email relay: An email relay server is a more general term that refers to any mail server that forwards email messages, regardless of the protocol used.
  3. Proxy mail server: A proxy mail server is a type of relay mail server that acts as an intermediary between the mail client and the destination mail server, hiding the IP address of the mail client.

Examples of relay mail servers include:

  1. Microsoft Exchange Server
  2. Postfix
  3. Sendmail
  4. Exim
  5. OpenSMTPD
  6. Mailgun
  7. Sendgrid

In summary, a relay mail server is a crucial component of email infrastructure that helps to ensure the reliable and secure delivery of email messages between mail clients and destination mail servers.