I recently converted a normal user mailbox into a shared mailbox and granted two individual users Full Access and Send As permissions. However, I'm running into issues sending emails from the shared mailbox in the Outlook desktop app. In this setup, we have Microsoft 365 and Exchange Online, and I've confirmed the permissions through PowerShell. The odd part is that while replies from the shared mailbox work fine, I can only send new emails successfully when I select the From address from the Global Address Book. If I try to use the recent dropdown, I get a SendAsDeniedException (EC 1244) error stating I don't have permission. Interestingly, sending emails from the shared mailbox works flawlessly through Outlook Web. How can I fix this so the users can send emails from the shared mailbox without issues?
4 Answers
Make sure you also update your offline address book. Try going to the Send/Receive tab, then choose Send/Receive Groups, and select Download Address Book. Ensure that "Download changes since last Send/Receive" is checked. If that doesn’t solve it, you might need to create a new Outlook profile. OWA works directly because it queries the server every time and doesn’t rely on the local cache like the desktop app does. Good luck!
You might want to check how long it’s been since you assigned those Send As permissions. They usually should take effect pretty quickly, but I've seen it take up to 48 hours occasionally. If it’s been that long, you could remove the users and then re-add them. Just be sure to wait a bit before testing again.
We've faced this issue too. Microsoft has mentioned that they aren’t going to fix this right now, so you might need to get everyone used to selecting the from address from the address book. A workaround we found is that sometimes if you manually add the shared mailbox again, it creates a cached entry in the dropdown that might actually work without the X to delete it. Just something to keep in mind!
It sounds like you're dealing with a caching issue in your Outlook client. Since email sends are functioning when selected from the address book and OWA is working fine, I’d recommend clearing the cache for that shared mailbox. You can do this by creating a new email, clicking "From," and if the shared mailbox appears in the recent list, hover over it and click the small X or “Remove” icon to delete it. After that, try adding it back normally and send a test email to check if the problem persists.
Thanks for the tip! I've tried this, but the same issue occurred when selecting from the recent dropdown. I also tried creating a new profile, but no luck.
It's only been about 4-5 hours since I set the permissions. Everything else seems to work fine; this is just a specific scenario where I'm hitting a wall.