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Can someone explain the connection (or disconnect) between the Alias field in the General tab of a user's Exchange properties and the SMTP addresses (Email Addresses tab)?

The terminology has me confused:

  • SMTP address
  • Alias
  • Proxy address
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up vote 3 down vote accepted
  1. The SMTP address is simply the full e-mail address:
  2. The alias is used by Exchange to find any local object with an e-mail address. So even before Outlook caches the address in the NK2 file, if you have an alias of Kevin for a local user or object (other items can have e-mail addresses associated with them, like public folders, or external contacts, for example), just putting in kevin in Outlook's "To:" field will make it resolve and go to him.
  3. The term proxy address does not come up often in practical use, but it is the e-mail address a foreign system recognizes you as, usually your SMTP address. Here is an article:
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  1. The SMTP address is the primary SMTP address of the mailbox enabled user object or mail enabled object (as opposed to additional SMTP addresses or an X.400 address or a Microsoft Mail address, etc).

  2. The alias is an Exchange attribute of the mailbox enabled user object and is generally used when connecting to the mailbox via POP. The alias and the user logon name must match in order to access the mailbox via POP. The alias can also be used when sending email to the mailbox enabled user (as opposed to using the full SMTP address).

  3. A proxy address is any email address other than the primary SMTP address. Examples of proxy addresses are: additional SMTP addresses, Microsoft Mail addresses, X.400 addresses, etc.

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Alias is mostly irrelevant and based on legacy Exchange from the days before SMTP was the default address. It usually defaults to username and once set you shouldn't change it (due to Outlook to: line autocomplete cashing). Doesn't really matter what alias is. Used internally by Exchange and usually not seen by users. Never seen by external users.

SMTP is their primary address and has to be unique. You can set more then one for a mailbox, but the one set default will be their reply-to address.

Not sure about proxy address, where do you see that?

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The alias isn't irrelevant and is does matter what it is. If you're connecting to your mailbox via POP and the alias doen't match the user logon name you won't be able to connect. – joeqwerty Jun 2 '11 at 14:34
wow that's an interesting quirk. Thanks joeqwerty. I recently ran some tests on Exchange 2010 and found that you could even have multiple users with the same alias and all seemed to function correctly. Had wondered if it did anything anymore other then map to user in Outlook. – Bret Fisher Jun 2 '11 at 14:38
It is quirky. I don't know if it's a bug (if it is it's been around for a long time) or if that's the intended behavior. – joeqwerty Jun 2 '11 at 14:58

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