The error is clearly telling that tls v1.2 is required. And @Tim_Parnell has it setup like that. Only xojo may give the correct answer or you can wireshark the connection and try an findout what’s happening.
@Tim_Parnell does this make a difference?
Dim con As new SMTPSecureSocket
con.Address = "smtp.office365.com"
con.Port = 587
con.Username = ""
con.Password = ""
con.SSLConnectionType = SMTPSecureSocket.SSLConnectionTypes.TLSv12
con.SMTPConnectionType = SMTPSecureSocket.SMTPConnectionTypes.STARTTLS
con.SSLEnabled = True
// Create an email message, use the SendMail method only. Don't call .Connect
break
How about the email headers, are they confirming tlsv1.2 ?