In the new message window, above the To... button, click From Click the account that you want to use. You can add the "From" address by clicking on From, then "Other E- mail Address" and finding the account name in the address book. 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