How do I solve [EIdSMTPReplyError] Authentication unsuccessful? - delphi

Question

I'm trying to use SMTP with TLS and Office365. I'm able to successfully send an email using powershell and TLS but with the below example I'm currently stuck with error:
Project SMTP_SSL_Example.exe raised exception class EIdSMTPReplyError
with message 'Authentication unsuccessful
[JN2P275CA0026.ZAFP275.PROD.OUTLOOK.COM]'
The connection is successful but the authentication part in the code fails. I've previously been told that the response is coming from the server. If I get a successful mail using PowerShell how come this differs? Any ideas?
I'm using Indy 10.6.2.5366.
Update: I'm also getting the same kind of error with another component suit. I just don't understand why Powershell is allowing me to send the mail but I can't programmatically.
procedure TForm28.Method2Click(Sender: TObject);
var
idSMTP1: TIdSMTP;
idSASLLogin: TIdSASLLogin;
idUserPassProvider: TIdUserPassProvider;
begin
idSMTP1 := TIdSMTP.Create(nil);
try
idSMTP1.IOHandler := TIdSSLIOHandlerSocketOpenSSL.Create(idSMTP1);
idSMTP1.UseTLS := utUseExplicitTLS;
TIdSSLIOHandlerSocketOpenSSL(idSMTP1.IOHandler).SSLOptions.Method := sslvTLSv1;
idSMTP1.Host := 'smtp.office365.com';
idSMTP1.Port := StrToInt(cbPort.Text);
idSASLLogin := TIdSASLLogin.Create(idSMTP1);
idUserPassProvider := TIdUserPassProvider.Create(idSASLLogin);
idSASLLogin.UserPassProvider := idUserPassProvider;
idUserPassProvider.Username := 'my username';
idUserPassProvider.Password := 'my passowrd';
idSMTP1.AuthType := satSASL;
idSMTP1.SASLMechanisms.Add.SASL := idSASLLogin;
try
idSMTP1.Connect;
try
idSMTP1.Authenticate;
SendEmail(idSMTP1);
finally
idSMTP1.Disconnect;
end;
ShowMessage('OK');
except
on E: Exception do
begin
ShowMessage(Format('Failed!'#13'[%s] %s', [E.ClassName, E.Message]));
raise;
end;
end;
finally
idSMTP1.Free;
end;
end;
procedure TForm28.Mehod1Click(Sender: TObject);
var
idSMTP1: TIdSMTP;
begin
idSMTP1 := TIdSMTP.Create(nil);
try
idSMTP1.IOHandler := TIdSSLIOHandlerSocketOpenSSL.Create(idSMTP1);
idSMTP1.UseTLS := utUseExplicitTLS;
TIdSSLIOHandlerSocketOpenSSL(idSMTP1.IOHandler).SSLOptions.Method := sslvTLSv1;
idSMTP1.Host := 'smtp.office365.com';
idSMTP1.Port := StrToInt(cbPort.Text);
idSMTP1.AuthType := satDefault;
idSMTP1.Username := 'my username';
idSMTP1.Password := 'my password';
try
idSMTP1.Connect;
try
idSMTP1.Authenticate;
SendEmail(idSMTP1);
finally
idSMTP1.Disconnect;
end;
ShowMessage('OK');
except
on E: Exception do
begin
ShowMessage(Format('Failed!'#13'[%s] %s', [E.ClassName, E.Message]));
raise;
end;
end;
finally
idSMTP1.Free;
end;
end;

Answer 1

Office 365 will soon require TLS 1.2, but your code is forcing Indy to use TLS 1.0 instead. Office 365 officially does not support TLS 1.0 or 1.1 anymore, but it still accepts 1.0/1.1 sessions for the time being, but that will change in the coming months.
So, at the very least, you need to change this:
TIdSSLIOHandlerSocketOpenSSL(idSMTP1.IOHandler).SSLOptions.Method := sslvTLSv1;
To this:
TIdSSLIOHandlerSocketOpenSSL(idSMTP1.IOHandler).SSLOptions.Method := sslvTLSv1_2;
Or better, to this:
TIdSSLIOHandlerSocketOpenSSL(idSMTP1.IOHandler).SSLOptions.SSLVersions := [sslvTLSv1, sslvTLSv1_1, sslvTLSv1_2];
That being said, using TIdSASLLogin as the sole SASL mechanism is exactly the same as using TIdSMTP.AuthType=satDefault. They both send the same AUTH LOGIN command to the server. And that command is what is failing. But there is no way to know for sure exactly why that is happening. "Authentication unsuccessful" is too generic an error message, and there are many reasons why that error occurs in Office 365. Maybe you are using the wrong username/password. Maybe the IP address resolved from the hostname being sent by TIdSMTP in its EHLO command 1 is not whitelisted on the server. Who knows.
1: try setting the TIdSMTP.HeloName property to a FQDN for your client machine, which you can get from GetComputerNameEx().