Sporadic issues with smtp.office365.com 587

Sporadically I get:

Send-MailMessage : Unable to read data from the transport connection: net_io_connectionclosed.
At line:1 char:1

+ Send-MailMessage -to "kcadmin@receptrx.com" -from "kcadmin@receptrx.c ...

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (System.Net.Mail.SmtpClient:SmtpClient) [Send-MailMessage], SmtpExcept
   ion
    + FullyQualifiedErrorId : SmtpException,Microsoft.PowerShell.Commands.SendMailMessage

When trying to send emails from a Windows 2016 Server (set up in vSphere).

Sending emails from/to the same domain. Used:

Send-MailMessage –From <O365 email address> –To <Recipient email address> –Subject "Test Email" –Body "Test SMTP Service from Powershell on Port 587" -SmtpServer smtp.office365.com -Credential $creds -UseSsl -Port 587

Send-MailMessage -From <O365 email address> -To <Recipient email address> -Subject "Test Email" -SmtpServer smtp.office365.com -Credential $creds -UseSsl -Port 587

What I have tried:

1. Disabled the firewall.

2. Created Inbound Rule for 587.

3. Tested Telnet and received:

   451 5.7.3 STARTTLS is required to send mail [SA9PR13CA0131.namprd13.prod.outlook.com]

If I execute the same script on another server (Windows Server 2019 in vSphere, I don't get the same issues. Both servers are in the same network/domain.

Any suggestions as to what else should I try?