Is there a technical name for the two halves of an email address? I mean the parts before and after the @ sign.

As a kind of example of what I mean, for UK postcodes, I believe the two halves are called the inward and outward, not by the general population, but by people who work with postcode data.

  • For UK postcodes the terms are inward and outward, based on the idea that the first half indicted the sorting office where post would go in from other sorting offices, before going out to individuals.
    – Henry
    Feb 13, 2012 at 12:56
  • @Henry, you're right, i couldn't remember it exactly and couldn't find a reference. i'll edit
    – hawbsl
    Feb 13, 2012 at 12:59
  • Rightly belongs on the SO site?
    – Kris
    Feb 13, 2012 at 13:03

1 Answer 1


Yes, although it is not commonly mentioned, even in Computer Science:

The part before the @ sign is the local-part of the address, often the username of the recipient (jsmith), and the part after the @ sign is a domain name to which the email message will be sent (example.org).

from the wikipedia article.

  • 2
    Might as well link to the canonical document: tools.ietf.org/html/rfc3696#section-3 which says "Contemporary email addresses consist of a "local part" separated from a "domain part" (a fully-qualified domain name) by an at-sign ("@")."
    – slim
    Feb 13, 2012 at 12:52
  • Yup, note that this notation is inspired from unix login notation, for example if I want to log in as user dvador to google.com through ssh, I will type: ssh [email protected]
    – Vladtn
    Feb 13, 2012 at 13:02
  • SMTP/UUCP email predates SSH by quite a long time. SSH here is borrowing convention from those.
    – slim
    Feb 13, 2012 at 13:10

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