RecipientStatus RESOLVER.GRP.Expanded; distribution list expanded

Question

Hi. Exchange 2019. On-premise.

There's a mailing list group. It has permission to receive mail from the Internet.

Everything works, but one email didn't arrive.

Timestamp : 7/24/2024 2:39:00 PM

ClientIp :

ClientHostname : MS-EX01

ServerIp :

ServerHostname :

SourceContext :

ConnectorId :

Source : ROUTING

EventId : DROP

InternalMessageId : 212626650959119

MessageId : <6FB3FCD2030EA34FA92D53F17ED010F4013622@MANUSCRIPT3.kommersant.local>

NetworkMessageId : abcf3452-75c6-43a6-ea75-08dcabd5354c

Recipients : {pr@Hidemydomain.com}

RecipientStatus : {[{LED=250 2.1.5 RESOLVER.GRP.Expanded; distribution list expanded};{MSG=};{FQDN=};{IP=};{LRT=}]}

TotalBytes : 25097

RecipientCount : 1

RelatedRecipientAddress :

Reference :

MessageSubject : вопросы для комментария

Sender : Yakushko@kommersant.ru

ReturnPath : Yakushko@kommersant.ru

Directionality : Originating

TenantId :

OriginalClientIp :

MessageInfo :

MessageLatency :

MessageLatencyType : None

EventData : {[DeliveryPriority, Normal], [AccountForest, MyFQDN]}

TransportTrafficType : Email

SchemaVersion : 15.01.2507.039

I found information here that the group is closed. But it's open.

https://www.exchangelog.info/2023/08/reason-led250-215-resolvergrpexpanded.html

PS C:\Windows\system32> Get-DistributionGroup -Identity "PR@mydomain.com" | Format-List Name,RequireSenderAuthenticationEnabled

Name : pr

RequireSenderAuthenticationEnabled : False

How can I understand for what reason the message is DROP ?