When installing WirelessMail, there is no value available for the forwarding address, and the field is not editable. Installation cannot continue without a value.
To resolve this problem, on the Installation screen, click the Advanced button. In the File Name field, change the .nsf to .NSF and then click out of the field. This will make the forwarding address field editable. Enter your forwarding address and then click Install WirelessMail.