Having trouble sending group messages or forwarding group messages in Windows Live Mail, Hotmail account.

Every time I send or forward a group message, I get the following error:

Generating server: CO2PR17MB0137.namprd17.prod.outlook.com

;
Remote Server returned '550 5.1.3 STOREDRV.Submit; invalid recipient address'

Original message headers:

Received: from CO2PR17MB0137.namprd17.prod.outlook.com ([10.161.84.26]) by

 CO2PR17MB0137.namprd17.prod.outlook.com ([10.161.84.26]) with mapi id

 15.01.0619.011; Wed, 21 Sep 2016 19:51:09 +0000

Content-Type: application/ms-tnef; name="winmail.dat"

Content-Transfer-Encoding: binary

From: =?iso-8859-1?Q?Marco_=3F=3F?= <*** Email address is removed for privacy ***>

To: ";" <;>

Subject: Test

Thread-Topic: Test

Thread-Index: AQHSFEF/YYQy5HuEY0mMwLW42hdO6A==

X-MS-Exchange-MessageSentRepresentingType: 1

Date: Wed, 21 Sep 2016 19:51:09 +0000

Message-ID: <*** Email address is removed for privacy ***>

Accept-Language: en-US

Content-Language: en-US

X-MS-Has-Attach:

X-MS-TNEF-Correlator: <*** Email address is removed for privacy ***>

MIME-Version: 1.0

All the recipient addresses seem to be correct.  I have used them many times without any problem.  I don’t know why this started now.

I have tried sending it to myself.  When I send this e-mail, the sender’s name returns “Sender Name ??”  I also don’t know what this means.

I cannot seem find what is generating this error.

Any workable solution would really be appreciated.

Thanks.