Assuming that email was sent via outlook or any other client other than webmail this error is appearing, the resolution would be to remove the email address from the group and re-add it to the group.

However, due to security reasons I can’t add certain details here, I would request you to please open a support case with AWS using the following link.

https://support.console.aws.amazon.com/support/home?#/case/create

Hi there -- thank you for your interest in Amazon WorkMail!

That 'invalid recipients' error can occur if you have a cached contact in your auto-complete addressbook that refers to an address which no longer exists. The addressbook or contact is stored by Outlook, and if this happens, you just need to clear it out and let it recreate automatically the next time you email that person. For example, if you are writing to a contact named alice@example.com, and the 'alice' email box was deleted, but later, a new 'alice' was created, the internal reference will have changed, and you may see that message; if you clear the old 'alice@example.com' out and then reply to Alice's email, it will add a new, valid 'alice@example.com.'

If you are sending to an individual contact, in Outlook, please try typing the address and letting the autofill complete it, but don't click or hit return. When it shows the suggestions in the drop-down, hover your mouse over one and you should see a small 'x' on the right side. Clicking the 'x' will clear it. To email that person the next time, you will have to re-type the recipient's SMTP address or reply to an email from them, but it should deliver normally from that point. If you think this affects multiple contacts, you can also clear the entire list. (See Outlook docs for more.)

If you are sending to a contact list that you created manually in your Contacts, then you can navigate to open the list and look through the contacts in it, and find the one or ones that need clearing and recreating. Unfortunately, I believe contact lists do not refresh even if the underlying contact is fixed, so it might mean a little trial and error to figure out which individual contact is the issue, or deleting the list and making a new one after you clear the old contacts, but the good news is that it should be fixable.

Kind regards,

Sabrina