Outgoing mailbox server

An outgoing mailbox server, also known as a mail submission agent (MSA), is a type of email server that is responsible for sending emails from a mail client or a mail user agent (MUA) to a remote email server.

Here's how it works:

  1. A mail client or MUA (e.g., Microsoft Outlook, Mozilla Thunderbird) connects to the outgoing mailbox server using the Simple Mail Transfer Protocol (SMTP).
  2. The mail client or MUA authenticates with the outgoing mailbox server using a username and password or another authentication mechanism.
  3. The mail client or MUA sends the email to the outgoing mailbox server, which then relays the email to a remote email server (e.g., a mail exchange server, MX record).
  4. The remote email server then delivers the email to the recipient's email account.

The outgoing mailbox server plays a crucial role in the email delivery process, as it ensures that emails are properly formatted, authenticated, and routed to the correct destination.

Some common features of an outgoing mailbox server include:

  1. Authentication: Verifies the identity of the mail client or MUA before allowing it to send emails.
  2. Encryption: Encrypts emails to ensure secure transmission.
  3. Spam filtering: Blocks or quarantines spam emails to prevent them from being sent.
  4. Virus scanning: Scans emails for viruses and malware before sending them.
  5. Content filtering: Filters emails based on content, such as keywords or attachments.
  6. Rate limiting: Limits the number of emails that can be sent per minute or hour to prevent abuse.

Outgoing mailbox servers can be implemented using various technologies, including:

  1. Microsoft Exchange Server
  2. Postfix
  3. Sendmail
  4. Exim
  5. OpenSMTPD
  6. Qmail

In summary, an outgoing mailbox server is a critical component of the email infrastructure, responsible for sending emails from a mail client or MUA to a remote email server while ensuring security, authentication, and proper routing.