Bounce backs on emails sent through Outlook Exchange account

[jmt356]

For several weeks, when sending new emails to email addresses on an Outlook Exchange Server, when I select a new email address from the Global Address List by clicking To... on a new email, the email results in a bounce back. Outlook states:

"The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk."

Then, under "Diagnostic information for administrators," a very long and odd string appears next to what I would expect to be the email address. It is as though Outlook is not sending the email to the address I place in the To field, but rather, is routing it to some other strange address.

This issue does not occur if I reply directly to an email that the recipient sent to me. It occurs when I send a new message, even if I copy the recipient's exact email address not the To field of a new message or select their email address from the Global Address List.