We have the following scenario,

Mailbox A: sales@ourdomain.com (roll based mailbox)
Mailbox B: asalesperson@ourdomain.com (an actual person's mail)

Mailbox B accesses Mailbox A through Mailbox A forward and Mailbox B rule.

Now I need to add a persona for Mailbox B that allows them to send mail using the MailBox A from address. According to a different post, I needed to enable "Allow sending from any address" in their settings.

After I did that, I expected the drop down box that shows all of their aliases to contain all of the e-mail address or allow them to enter an email address in a text box. However, once I logged the user in and went to create a new persona, I still couldn't find a way to set the From address (not the Reply-To address) to sales@ourdomain.com.

Can someone shed some light on this for me? Is there a work around, a known issue or applicable bug?