Outlook 2016 Win-10 Cannot send email to one address

Hello,
Started getting the following error while trying to send email via Outlook 2016. Tried to send to the same email from WebMail and was able to do so. Mail provider says (i think they're right) its an Outlook issue.

Windows - 19042.1110, 20H2
----------------------------------------------------
Your message did not reach some or all of the intended recipients.
Subject: my subject
Sent: x/xx/2021 xx:xx PM
The following recipient(s) cannot be reached:
xxxxxxxxx@hotmail.com on x/xx/2021 xx:xx PM
None of your email accounts could send to this recipient.
---------------------------------------------------------


I cleaned out the "Auto-Complete List".

Created new email and tried to get to the Email properties box but cannot get to it. I always land up with:




For other emails, from Email properties, I get the following box



From File-Headers, I got
From: "System Administrator"
Sender: "System Administrator"
To: "xxxxxx@hotmail.com"
Subject: Undeliverable: Test-mail
Date: Mon, xx Jul 2021 xx:xx:xx -0400
Message-ID: xxxxxxxxx@Domain
MIME-Version: 1.0
Content-Type: application/ms-tnef;
name="winmail.dat"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="winmail.dat"
X-Mailer: Microsoft Outlook 16.0
Thread-Index: AQGTablbCbJA3HVIhGk3qw2pAFhAXA==
X-OlkEid: 00000000C2D58FF8FA005E46A927E31281E18B880700D9539C2261A6BB45B9DAB62C7081B3C101002200FFFF000048B20E36 E1573D45B48BB74AFE9B1BE6000000000414000066B0BC4B166A1A42960053758F
X-MS-TNEF-Correlator: 00000000C2D58FF8FA005E46A927E31281E18B880700D9539C2261A6BB45B9DAB62C7081B3C101002200FFFF000048B20E36 E15BE60000000004140000
X-Antivirus: Avast (VPS 210712-0, xx/xx/2021), Inbound message
X-Antivirus-Status: Clean

While googling, I did see some similar situations but none of the fixes worked for me

Yes, I did type in manually and I'd also cleared Auto-Complete List and then tried but no luck.

Yes, eyesight isn't good but it isn't as bad either no typos here