Hi! I'm still having this kind of issue Outlook : Office 2011 for Mac error (17099) I tried to search and perform some troubleshooting steps to resolve this issue, still not resolve the issue (Already tried to check and re edited the email addresses that included in the group message) (Already deleted the message that got stuck on Outbox in Offline Mode) (Already contacted my ISP) but still having the same issue, It will be highly appreciated if you can help me or give me some tips.