Does the part to the right of at sign have to be valid website address?

Question

Does the part to the right of the at sign in email addresses have to be a valid website url? I just saw two email addresses where the right part didn't look to be a website address. In fact, it didn't open when I tried to do so via a web browser.

Answer 1

No it does not have to be the same. Email uses a different protocol than websites, and there's always the option to have non-existing domains for internal emails (inside companies).

For example, if I have a domain controller which hosts MyDomain.local, and I have an exchange server inside this domain, I can have [e-mail]

If I do not host a webserver and disable everything else that makes websites, http://MyDomain.local will not work.

On top of that, given that this is an internal address only, it will not work from the outside either.

If we talk about external email addresses, then the following matters:

The email address has 2 parts: the user and the domain + optionally subdomains.

If we take for example: [e-mail], then LPChip is the user, email is the subdomain and example.com is the domain.

The domain has MX records that tell where email is located. It is this route that is used to deliver email by the SMTP protocol.

Now its also possible to have an @ in a website url which usually means username@website but can also be used as @ char in the website's uri.

For example, the following website address is valid: https://example.net/owa/[e-mail]

The uri here is /owa/[e-mail] and does contain a @.

Another example is this:

ftp://[e-mail]

Answer 2

No, website and email address have basically nothing in common.

The right part of [e-mail] means that you send email to a domain called microsoft.com. The protocol used to send email is SMTP.

But the url http://www.microsoft.com/ means you want information that are hosted on a server called www. The protocol used is HTTP.

It is not required that these two parts exists for both protocols. And the contrary is also valid. For example, you may have a support website like http://support.dell.com/ and have no email address whatsoever @support.dell.com.

Answer 3

[e-mail] is a working email address if the MX record for example.org points to a working mail server that accepts mail for that email address (i.e. listening on port 25 and handling SMTP requests).

http://example.org/ is a working URL if the A record for example.org points to a host running a web server (i.e. listening on port 80 and handling HTTP requests). If there is no web server at example.org, most browsers follow the standard recommendation to also try http://www.example.org/.

Look up the relevant Internet RFCs, e.g. for TCP where it explains ports, if you want more details.

These are two different services that are completely separate. A server might be running one or both.

As Tersosauros points out, "valid" has a technical meaning of not-a-syntax-error, not necessarily "working". See that answer for more.

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Email is special in terms of DNS. MX records can list any mail server as the Mail-Exchange for a domain name. All other services (ssh, ftp, http, https, etc. etc.) use the A (IP Address) record directly, rather than first checking a "what's the FTP server for example.org" record for an extra layer of indirection. This is irrelevant for this question, though. All Internet services are orthogonal, and might or might not be present for any given domain name.

(port-based routing by a router/firewall can split up the http and the ftp traffic (for example) to different servers for a single IP if needed for large sites, so other services aren't missing out from not having their own indirection records like email does.)

Answer 4

The OP (and perhaps some of the commenters/answers) may be confused in vocabulary.

A valid website url (while trying not to be too pedantic) could be one of two different things:

1. A valid format URL (URI in the modern lexicon), such as abc://azertyfoo.baz:303/ - this however is NOT a web address.
2. A URL that is both syntactically valid (as above), but also specifies a known scheme (the bit before ://), AND names a valid resolving fully-qualified domain name (FQDN). For example: http://superuser.com:80/ is a valid website URL (under these conditions).

Plenty of other answers have addressed the differences in DNS records with regards to web (i.e. A records) versus email (MX records).

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I suspect that where people perhaps are getting confused may be with the host portion of the email address.

A host may be any of the following in an email address:

• An FQDN, properly configured with MX records.
• An otherwise resolvable domain name that may not be fully qualified (as used in many corporate environments). For example MyMail.local - obviously .local is not a valid top-level-domain (TLD), however this domain name is still valid and may resolve in a corporate environment.
• A hostname, such as localhost (the default address on error pages in many versions of Apache is webmaster@localhost, for example). Nobody beyond the local machine will be able to ever send mail to that inbox, however, on that machine (assuming it is running sendmail or similar), the address is valid.
• an IP Address, 127.0.0.1 - again this is valid in a particular environment. However I doubt many (or any?) mailservers would forward mail to that host if you attempted this on the open Internet.

Any of these valid hosts may also be a valid website url if enclosed in an appropriate scheme and path: http://[any of the above]/