Distribution List Email failed and I don't understand why

[PetsforVets]

We are a non-profit with limited IT experience, so please be kind with responses.  Hoping you can provide some guidance to assist with how to fix this.

Tried to send an AllCompany email to the distribution list and it wasn't delivered.  Message trace text included:

Received -> Not Processed -> Not delivered

2/23/2024, 6:43 PM | Drop | Reason: [{LED=554 5.4.184 RESOLVER.GRP.SuppressYammerGroupExpansion; By design group expansion for Yammer groups is suppressed so posts are not sent to the group members mailboxes};{MSG=};{FQDN=};{IP=};{LRT=}]

[#2]

You cannot use the AllCompany Yammer group to send emails. You can create a "traditional" Distribution group instead, a dynamic DG or a "modern" Microsoft 365 Group (either with assigned members or dynamic one). Basically, use anything other than Yammer's built-in AllCompany :)