"The email address '<EmailAddress>' is unknown" error message when you add a user to a Windows SharePoint Services 3.0 or Windows SharePoint Services 2.0 Web site

When you add a user to your Microsoft Windows SharePoint Services 3.0 or Windows SharePoint Services 2.0 Web site, you may receive the following error message:

This issue occurs if all the following conditions are true:

• Windows SharePoint Services 3.0 or Windows SharePoint Services 2.0 is configured to use Active Directory account creation mode.
• The e-mail settings on the server are configured to use the Simple Mail Transfer Protocol (SMTP) service that is installed when you installed E-mail Services on the server to configure the server as a mail server.

In this situation, only the recipients who have mailboxes that are configured to use the Post Office Protocol (POP3) service can retrieve e-mail messages from the server. The SMTP server blocks e-mail messages that are sent to recipients who do not have mailboxes that are configured to use the POP3 service.

To work around this issue, configure Windows SharePoint Services 3.0 or Windows SharePoint Services 2.0 to use an SMTP server that lets users send e-mail messages to the recipients that they have to send e-mail messages to. To do this, follow these steps:

Windows SharePoint Services 3.0

1. Start SharePoint Central Administration.
2. Configure Windows SharePoint Services 3.0 to use a different SMTP server. To do this, follow these steps:
   1. On the Windows SharePoint Services Central Administration page, click the Operations tab, and then click Outgoing e-mail settings.
   2. On the Outgoing e-mail settings page, specify an SMTP server that lets users send e-mail messages to the recipients that they have to send e-mail messages to.
   3. Click OK.

Windows SharePoint Services 2.0

1. Start SharePoint Central Administration.
2. Configure Windows SharePoint Services 2.0 to use a different SMTP server. To do this, follow these steps:
   1. On the Windows SharePoint Services Central Administration page, under Server Configuration, click Configure default e-mail server settings.
   2. On the Configure E-Mail Server Settings page, specify an SMTP server that lets users send e-mail messages to the recipients that they have to send e-mail messages to.
   3. Click OK.
3. Configure the virtual server e-mail settings to use a different SMTP server. To do this, follow these steps:
   1. On the Windows SharePoint Services Central Administration page, under Virtual Server Configuration, click Configure virtual server settings.
   2. On the Configure Virtual Server Settings page, click the virtual server.
   3. On the Virtual Server Settings page, under Virtual Server Management, click Virtual server e-mail settings.
   4. In the Mail Settings area, specify an SMTP server that lets users send e-mail messages to the recipients that they have to send e-mail messages to.
   5. Click OK.

When you use Active Directory account creation mode, you can automatically create new accounts for users in Active Directory instead of using preexisting domain accounts. For example, an Internet service provider (ISP) may want to allow Windows SharePoint Services 3.0 Web site owners or Windows SharePoint Services 2.0 Web site owners to create user accounts or invite users to collaborate on a Web site where existing domain accounts for those users do not already exist.

For more information about how to install, configure, and administer Windows SharePoint Services 2.0, see the Microsoft Windows SharePoint Services Administrator's 2.0 Guide. To view the Microsoft Windows SharePoint Services 2.0 Administrator's Guide, visit the following Microsoft Web site: For more information about Windows SharePoint Services, visit the following Microsoft Web site: