Components of an Email System

Part 2 of “My Own Email Address”.

Plenty of articles list some steps to set up email at your own domain. It’s harder to find one that explains the principles of how it works, various ways to do it, and the pros and cons of each way.

The components we need are:

  • a registered domain name
  • domain name service (DNS) records
    • to direct incoming mail to my mailbox (or redirection service)
    • to prove the authenticity of outgoing mail
  • an SMTP server
    • to send outgoing mail
  • a mailbox (containing an “in-box” and other folders)
    • to receive incoming mail
    • to hold all my mail for this account (received, sent, drafts, etc.)
    • with IMAP and/or POP interface
  • (optional) a Web mail user interface
    • to send mail and access the mailbox from a web browser

The mailbox is the heart of a standard mail system. It is notable that the SMTP server for sending mail is a separate component.

Alternatively, instead of a mailbox, I could use

  • a redirection (forwarding) service

to redirect incoming mail addressed to my domain to an existing mailbox at another domain, such as my Gmail account. This kind of forwarding is not like the “Forward” function in an email client, but rather passes each incoming email message to a new server without altering the body text or subject or “From” header or (more or less) any other headers. The target mailbox will thus receive messages whose “To” address contains my domain name, not that mailbox’s domain name. The mailbox has to be willing to accept this.

No matter whether I choose to set up a separate mailbox or redirect mail into my Gmail account, my incoming and outgoing mail will look the same to other people: they will see my own email address not Google’s. It would just make a difference to the email headers which are normally hidden from view in most people’s mail readers.

The choice will, however, greatly affect how I read and manage my mail.

Each component listed above is conceptually separate, and in practice can be hosted and administered independently. However, it is usual to host some of them together, which tends to make administration easier.

I currently have both my domain registration and my DNS (as well as my web site) hosted by Andrews & Arnold. It’s usual for the mail-specific components (SMTP, mailbox with IMAP/POP interface, web interface) to be hosted by the same provider. When using redirection, however, some services support redirection of incoming mail but not SMTP for outgoing mail.

The components need to co-operate. In particular:

  • The registered domain name has an “NS” (name server) record attached to it, which tells everyone which DNS server controls the DNS records for this domain.
  • The DNS server holds the DNS records that describe all services attached to this domain name: web server, email, and anything else. For email, we need to put in “MX” records that tell other mail servers how to reach the mailbox (or redirector) for incoming mail, and other records for authentication and configuration.
  • The SMTP server needs to be willing to send mail identified as being “from” my domain name, and to “sign” it as such. It used to be common for any SMTP server that you were authorised to use, to be willing to send anything you asked it to send, but in recent years they have been much more locked down to control spam and abuse. In particular, I can’t use free Gmail account’s SMTP server to send mail from my domain name. (If I paid for a Google Apps account then it would let me do that.)
  • The mailbox needs to be willing to accept mail addressed to my domain. Of course if it’s a mailbox set up for this purpose then it will do. If I want to redirect mail addressed to my domain to my Gmail mailbox, however, I’ll need to check if Gmail will accept it.
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