In the new message window, above the To... button, click the From button. If you do not see the From button, go to "Options" along the top of Outlook and click the From button from there to add it. If you have previously sent a message from that other email account, it should be listed below your own email address and you can click on it to select it. If you have not sent from that other address before, add it to your From list by clicking "Other Email Address..." and then clicking "From". Then find the account name in the address book. Be sure to change the Address Book field to "Global Address List" and NOT the "Offline Global Address List". Important: Do not type in the actual email address, but instead find it in the address book by searching for it by name. You can now send your message and it will come from the NSCC account that you chose. You will find that the message will likely be in your own 'Sent Items' folder. You may drag and drop that sent message to the other mailboxes 'Sent Items' folder if you wish. Note: You must already have been given permissions from Digital Innovation & Technology Services to that account before you can send from it. Is the 'From' button missing? If you don’t see the From button, you can add it: Create a new email message. Select Options, then select From in the Show Fields group on the ribbon. Having trouble sending mail from the other mailbox? You may have to manually update the address book in Outlook in order to get it to work. Follow these steps to update your Outlook address book. https://support.office.com/en-us/article/change-the-account-used-to-send-email-messages-2bdd8d4f-e30f-4ec8-88a0-406ce7b23cc5 More info: https://support.office.com/en-us/article/open-and-use-a-shared-mailbox-in-outlook-d94a8e9e-21f1-4240-808b-de9c9c088afd?WT.mc_id=365AdminCSH&ui=en-US&rs=en-US&ad=US