This is happening only recently, failure from my hotmail acct. When I originate email from my gmail account, it works OK.
Diag from microsoft
Diagnostic information for administrators:
Generating server: CO1PR02MB8853.namprd02.prod.outlook.com
Receiving server: CO1PR02MB8853.namprd02.prod.outlook.com
Total retry attempts: 28
5/8/2022 11:32:06 PM - Server at CO1PR02MB8853.namprd02.prod.outlook.com returned '550 5.4.300 Message expired -> 421 4.4.2 Connection dropped due to SocketError'
5/8/2022 11:15:15 PM - Server at tmo-west.mx.a.cloudfilter.net (220.127.116.11) returned '421 4.4.2 Connection dropped due to SocketError'