If you got this error checking the mail flow for a distribution group, it means the distribution group is closed and only internal senders can send e-mail to this group. When outside user sends e-mail to this group you get Reason: [{LED=250 2.1.5 RESOLVER.GRP.Expanded; distribution list expanded};{MSG=};{FQDN=};{IP=};{LRT=}] Set Delivery for this group to internal and external users and your problem will be solved.
An Exchange Online license was applied to the user before the Exchange GUID got synchronized from on-premises Active Directory. For synchronized accounts, having the Exchange GUID synchronized from on-premises is used to tell Exchange Online that the mailbox hasn’t been migrated yet, and is what allows customers to pre-license accounts prior to migration. From: My user has a mailbox both on-premises and in Exchange Online. So, in my case many times we get into situation where license is applied before Exchange GUID is synchronized to O365. I am using this script to check whether user has two mailboxes. Script closes Exchange session BEFORE it opens connection to Exchange Online as both use same commands. You can use Get-Mailbox both on-prem and Online, therefore it is crucial to close connection before you open other. # DISCLAIMER: # This code is provided "as is" without warranty of any kind, either express or implied, including but not limited to the implied warranties of