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%SECTION{summary}%The function of an email virtual domain is to allow mail to be received by a machine that does not have the same domain name as the email address.

Let't try to state that better / differently: If you want (or need) to receive email for an email address that doesn't match the domain name of your email server, you need to set up a virtual email domain (or address). You must also have the "owner" of the DNS you are using include a suitable MX record, i.e., such that if an email is looking for the address of your virtual email server, it gets pointed to the "real" email server serving your domain.

Aside: Note that although I want to make the statements above clear and reasonably concise, I don't mind stating the same thing in more than one way if it seems likely to help a newbie get the idea. After all, this will probably become the ...Beginner page (see About These Pages, and it is not intended to be a man page. (The ...Reminder page might be closer to a man page, but with syntax examples.)

<later>Explain how to create virtual domains (addresses) in Postfix, and maybe other MTAs.

See:

Contents

More About the Function of a Virtual Email Domain

Restating: Creating a virtual email domain means getting your MTA (e.g., Postfix) to accept email (for local delivery) for an email address that is not "native" to the machine hosting the email server.

Notes:

  1. In my writing so far, I'm a little hesitant about the use of virtual email domain vs. virtual email address. As I understand that better, or someone else does, this page may require revision.

  2. The reason I added "for local delivery" is that an MTA can accept mail for other email addresses for the purpose of relaying. (I do not intend to discuss relaying in any more detail on this page except to say that an open relay (a relay that will accept email from any non-native user) is not a good thing — it is a major contributor to the spam problem.)

  3. By "native" address I mean an address in the "real" domain of the email server. For example, if my email server's domain name is "mydomain.com", email addresses of the form <name>@mydomain.com are native while addresses of the form <name>@someotherdomain.com are not native.

  4. When you create a virtual email domain, ideally you will have the flexibility to create its mailbox (inbox) in a location other than the location (/var/mail) of the native mailboxes.

  5. I asked a question (in the email thread which sparked this page) as to whether creating a virtual email domain allows me to send email. I got the answer "Yes, with tools like smtp with auth and/or webmail on that server for example", but I'm not sure what that really means, or to state it differently, I'm not sure that setting up a virtual domain name to receive email has much to do with sending email from that domain. I guess I'll learn more as we go on.

  6. The virtual domain must be real in the sense that it must be a registered domain name, and the MX of that domain must point to the virtual mailserver that you are setting up, otherwise the virtual mailserver should reject all messages for that virtual domain, unless the email is authorized to use the virtual server as a relay.

How to Set Up Virtual Email Domains

in Postfix

<please fill this in, if you know how (or know something)> wink

in Sendmail

Just add this line to /etc/mail/sendmail.mc

FEATURE(`virtusertable', `hash /etc/mail/virtusertable')dnl

and add every domain to /etc/mail/local-host-names. Then fill /etc/mail/virtusertable in two columns: The first is the virtual address, and the second is the real user. This example

fake@emailPLEASENOSPAM.com andrei

will put into Andrei's inbox every mail sent to fake@emailPLEASENOSPAM.com

in ???

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Topic revision: r3 - 2004-03-01 - TomasNunez
 
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