I can successfully connect to smtp.office365.com with OAuth and browse a mailbox but when I go to send mail I get a "Blocked" error

I can give the code to a colleague and he can run it and it works fine from his machine in India. I receive the colleague's email test fine to an outside mail server, which is a GoDaddy hosted email machine. But, when I try to run it I get this error message from 3 different machines/servers:

The remote server returned an error: (500) Internal Server Error. {"code":"RequestBlocked","message":"Request is preemptively blocked. Early service protection triggered. Please try again after 6.775 seconds"}

This one is from a server with a static IP address that we've had for more than 10 years. I also get the same error from an Azure VM. That one does not have a static IP. I also have the issue with my development computer at home. Same error, all three machines. I performed these tests within the last 2 hours to my office365 email server.

See the code below:

(EDIT: removed tenant, EASendMail license code and other identifying info)

  Dim oServer As New EASendMail.SmtpServer("smtp.office365.com", 587)
  oServer.Protocol = EASendMail.ServerProtocol.ExchangeEWS
  oServer.User = strUserName
  oServer.Password = parser.AccessToken
  ' User OAUTH 2.0
  oServer.AuthType = ServerAuthType.AuthXOAUTH2
  'oServer.Port = 587
  ' Enable SSL/TLS connection,
  oServer.ConnectType = SmtpConnectType.ConnectSTARTTLS
  Dim oMail As New EASendMail.SmtpMail("<licenseCode>")
  ' Your office 365 email address
  oMail.From = strUserName
  ' Set recipient email address, please change it to yours
  oMail.To = "******@fabryfamily.com"
  ' Set email subject
  oMail.Subject = "test email from office 365 account"
  ' Set email body
  oMail.TextBody = "this is a test email sent from VB.NET project with O365"
  Dim smtp = New EASendMail.SmtpClient()
  smtp.SendMail(oServer, oMail)    'This is where the error occurs