Hello! I have the same problem except a different error code - just started this evening. I inadvertently removed a PST file that was associated with a live email account. The only way I knew how to get the email address associated back to the PST file was to delete the account and then add it in again to the existing PST file. It added fine and passed the Outlook tests and I can receive emails but when I try to send the emails I get the following System Administrator Error below. I tried Tony Chen's suggestion to type the email address again instead of using the autocomplete and still same response. I deleted the account again and re-added it with associating it with the existing PST file and same response, even though both times it passed the Outlook tests for sending and receiving. Any help is appreciated! Thank you!!