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I receive all email to my domain regardless of user via a catchall address.

I would like to be able to send mail from outlook via any ad-hoc address I create.

Eg, if there is a new website i might sign up with I would receive the email via a catchall.

But I need to be able to easily send via that catchall as well.

I tried the "Send As" Domain permission as described in User to send as anyone in Exchange? and then used the "From/Other email address" feature in Outlook 2010, but the mail bounces at my server with the error:

"You can't send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk."

I suspect it failed because I don't have actual User accounts for the address I'm using.

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I suspect the same thing. You can't send as a user that doesn't exist. It's a typical error message, with lots of information, none of it useful.

It makes sense to simply create the user before you send as that user.

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There is a way to do what you are describing BUT it requires setting up separate accounts in Outlook.

I'd like to use your example above and expand upon that. Assuming that is your main email account that is configured as a catchall mailbox for your domain. Let's also assume that you have Outlook configured to send and receive email from that address.

Although the mailbox described above will receive emails to any username at you will still only be able to SEND as In order to be able to send mail as, for example you have to add a second, new account to your Outlook configuration.

Go to Tools--->Account Settings and select the E-mail tab. Click New... and select Pop3 and hit Next>

Enter the name and email address that you want to send email as. Example:
Your Name: Sales Director
E-mail address:
Don't worry about password at this point. We will override password settings in a subsequent step. Hit Next>

Auto Configuration will fail at this point. That is OK. Click Manually Configure E-mail Settings and hit Next>

User Information
Your Name: Sales Director
E-mail Address:

Server Information
Incoming mail server: localhost (this is an outgoing-only account incoming is handled by catchall)
Outgoing mail server (SMTP): (provide smtp server hostname here)

Login Information
User Name: sales
Password: (leave blank)

click More Settings...

in the Internet E-mail Settings dialog click the Outgoing Server tab
check the checkbox for My outgoing server (SMTP) requires authentication
click the radio button for Log on using
User Name:
Password: (your password for

Save all chagnes and test settings. Incoming mail service will FAIL for this account. That is ok because is already your incoming mail catchall. it's essential however that your outgoing mail server passes ok. When this is done test your new address by opening a New E-mail Message in the send header you will see that you have the ability to select send From... multiple email addresses. Select and send yourself an email.

You will have to repeat this process and add additional accounts for every email address you want to send from.

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