Re: Cant send an email to a group unless we choose if from the group list

Hi Mahesh,

According to your description, this issue is probably caused by the Outlook nickname cache (AutoComplete). Please refer to the resolution in the following kb:
"550 5.1.1 RESOLVER.ADR.ExRecipNotFound" NDR error message when you send email messages by using Outlook in Office 365

After resetting the nickname and the autocomplete caches in Outlook as suggested in the above kb, please type in the complete email address of your group when sending an email to this group.
If the issue persists, please post back. We will help you with further troubleshooting.

Thanks,
Allen Zhang