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ProtonMail SMTP Bridge Authentication Failed

Trying to send emails using SMTP via ProtonMail Bridge (https://protonmail.com/bridge). It basically acts as a local SMTP server for sending secure email.
When trying to send via my .Net application, Im getting:
System.Net.Mail.SmtpException: Authentication failed.
at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)
at System.Net.Mail.SmtpClient.GetConnection()
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at EmailTest.Form1.sendButton_Click(Object sender, EventArgs e) in D:\VisualStudio\EmailTest\EmailTest\Form1.cs:line 68
Heres my test code:
SmtpClient smtp = new SmtpClient();
smtp.UseDefaultCredentials = false;
smtp.Credentials = new NetworkCredential("<my username>", "<ProtonMail bridge password>");
smtp.Host = "127.0.0.1";
smtp.Port = 1025;
smtp.Send("me#FakeEmail.com", "them#FakeEmail.com", "Test Message Subject", "Test Message Body");
I will also get the same exception when trying
smtp.EnableSsl=true
When I take the exact credentials/configuration and put them into an email client (Outlook or alike) it works fine.
Has anyone encountered this issue before? Is there any type of workaround for this?
The only thing I can find when searching online is to make sure UseDefaultCredentials=false is set BEFORE setting the Credentials property. But Im already doing that.

According to ProtonMail support, this is a known compatibility issue and currently has no direct resolution.
I ended up switching from System.Net.Mail.SmtpClient to MailKit. It has all the same functionality and it works with the ProtonMail Smtp service

Why can't I send e-mail from a C# app when I can send e-mail from a mail client just fine?

I have a task to troubleshoot why a C# app is failing to send automated e-mail messages. I carefully checked the source code, and could find absolutely nothing wrong.
Therefore, I tried to send e-mail from Thunderbird, the e-mail client I normally use. I specified the same SMTP relay, the same UID and password, and everything worked fine.
Trying to isolate the problem, I tried writing a very short C# console app to see what might be going wrong. I wrote the following:
using System.Net;
using System.Net.Mail;
namespace ConsoleApp3
{
class Program
{
static void Main(string[] args)
{
var client = new SmtpClient("my.server.with.ssl", 465);
client.EnableSsl = true;
client.Credentials = new NetworkCredential("uid", "pwd");
var message = new MailMessage("me#example.com", "myemail#mydomain", "Test Message Subject", "Test Message Body");
client.Send(message);
}
}
}
I entered the same credentials that I used in Thunderbird. When I run the above, I get the following error:
Unhandled Exception: System.Net.Mail.SmtpException: Failure sending mail. ---> System.IO.IOException: Unable to read data from the transport connection: net_io_connectionclosed.
How can it be that e-mail is sent just fine from Thunderbird, but the simple programming above fails to work when I try to send an e-mail from a basic C# app?
Edit I tried changing the port number to 587 as suggested in the Question that #stuartd linked to, and in that case, I get an error that says The operation timed out.
Edit I've tried using other e-mail servers and adjusting the settings, but nothing works so far. I've tried connecting to the same SMTP server that I use for my personal e-mail and it shows an error that the connection times out.
Edit I can't say why, but everything seems to be working now in spite of the fact that I didn't change any code. It seems as if something odd happened with my connection.

try using the default constructor and specify the host only.
Also some servers require that the client be authenticated before the server sends e-mail on its behalf. Try changing the value of UseDefaultCredentials
var mail = new MailMessage();
mail.From = new MailAddress("xxx#gmx.net");
mail.To.Add("yyy#gmail.com");
mail.IsBodyHtml = true;
mail.Subject = "subject";
mail.Body = "content";
var client = new SmtpClient();
client.UseDefaultCredentials = false;
client.Host = "mail.gmx.net";
client.EnableSsl = true;
client.Credentials = new NetworkCredential("user", "pass");
client.Send(mail);
if that doesn't help than tell us the server name if its the public one

Try using:
SmtpClient smtpClient = new SmtpClient("mail.mymailhost.com");
smtpClient.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;

Sending mail using gmail and .net

Getting the exception:
Failure sending mail.
While using System.Net.Mail.Smtp
in C#.NET on the line smtp.Send(message);
System.Net.Mail.MailMessage message = new System.Net.Mail.MailMessage();
message.To.Add(sendto);
message.Subject = "CP1 Lab Password";
message.From = new System.Net.Mail.MailAddress("abc#gmail.com");
message.Body = mail_message;
System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient("yoursmtphost");
smtp.Host = "smtp.gmail.com";
smtp.Port = 465; //(465 for SSL)587
smtp.EnableSsl = true;
smtp.Credentials = new System.Net.NetworkCredential("abc#gmail.com", "mypassword");
smtp.Send(message);
Edit 1:
Here is the detail of the error:
A connection attempt failed because the connected party did not
properly respond after a period of time, or established connection
failed because connected host has failed to respond ...
The same error when using port 25.
Few months before this code used to work but today it is not working

As from your exception message (incomplete) and the code, it is very hard to say what went wrong in your case. Failure sending mail is thrown when the server is not found, port cannot be connected. It means that connection was not established, until now.
The exception message that gets raised if the connection was established but authentication was not performed correctly is, "The SMTP server requires an authenticated connection...". I would suggest that you check the PORT, SMTP server host (do not add http://) and then re-try. An SMTP connection (in most general cases) requires
SMTP Server host: smtp.gmail.com is enough!
PORT to connect at: I have always used default TCP port for SMTP, 25. It works.
EnableSsl: most require it. I suggest you always use it. client.EnableSsl = true;
Credentials are required by all: No server would allow bots sending emails. In this concern, if you create a new account. You may face trouble sending emails programmatically, I faced the problem with a new account not sending the emails whereas an old account (default account of mine) was sending the email without any trouble.
The following code template (if filled with accurate parameters) will definitely send the email, because I have tested and verified it bazillion times. :)
// You should use a using statement
using (SmtpClient client = new SmtpClient("<smtp-server-address>", 25))
{
// Configure the client
client.EnableSsl = true;
client.Credentials = new NetworkCredential("<username>", "<password>");
// client.UseDefaultCredentials = true;
// A client has been created, now you need to create a MailMessage object
MailMessage message = new MailMessage(
"from#example.com", // From field
"to#example.com", // Recipient field
"Hello", // Subject of the email message
"World!" // Email message body
);
// Send the message
client.Send(message);
/*
* Since I was using Console app, that is why I am able to use the Console
* object, your framework would have different ones.
* There is actually no need for these following lines, you can ignore them
* if you want to. SMTP protocol would still send the email of yours. */
// Print a notification message
Console.WriteLine("Email has been sent.");
// Just for the sake of pausing the application
Console.Read();
}
Sending an email may be a headache sometimes, because it requires some basic understanding of networking also. I have written an article that covers sending emails in .NET framework and a few problems that beginners usually stumble upon such as this one. You may be interested in reading that article also.
http://www.codeproject.com/Articles/873250/Sending-emails-over-NET-framework-and-general-prob

Cannot send email through Hotmail / live.com / outlook.com

I have read other answers on the stackoverflow. but none of the solutions work for me.
I'm trying to send email through live.com, but unable to it.
The error message:
mailbox unavailable. The server response was: 5.7.3 requested action aborted;
user not authenticated
or error message:
System.Net.Mail.SmtpException: Service not available,
closing transmission channel.
The server response was: Cannot connect to SMTP server 65.55.176.126
(65.55.176.126:587), NB connect error 1460
The code:
MailMessage mail = new MailMessage();
mail.From = new MailAddress("email#live.com");
mail.To.Add("someone#someone.com");
mail.Subject = "hello";
mail.Body = "awefkljj kawefl";
mail.IsBodyHtml = false;
SmtpClient smtp = new SmtpClient("smtp.live.com", 587);
smtp.EnableSsl = true;
smtp.Credentials = new NetworkCredential("email#live.com", "password");
smtp.Send(mail);
Are you able to send the email by using above code?
It works before, last year, but it is no more working now.
I'm not sure what has been changed to live.com email server.
What new settings or parameters should apply?

I ran into an issue where I was unable to send emails using the smtp.live.com SMTP server from certain hosts -- particulary Azure hosts. In my case, the SMTP attempt was from a host that I had never used to sign-in previously, so the attempt was blocked with the 5.7.3 error:
Mailbox unavailable. The server response was: 5.7.3 requested action aborted; user not authenticated
The solution was to browse to the account settings, locate the SMTP request in its recent activity, and select "This was me":

Tested and it works (different host address and a few other property set):
using (var client = new SmtpClient("smtp-mail.outlook.com")
{
Port = 587,
DeliveryMethod = SmtpDeliveryMethod.Network,
UseDefaultCredentials = false,
EnableSsl = true,
Credentials = new NetworkCredential(_sender, _password)
})
{
using (var mail = new MailMessage(_sender, _recipient)
{
Subject = _subject,
Body = _message
})
{
client.Send(mail);
}
}

Also, if the account has two-step verification turned on, you'll have to generate an app password and use that instead.

Your code works for me without any changes with a live.com address. I am able to generate the same exception by simply putting an incorrect password.
I would suggest following checks:
Did the user change password recently? Are you able to login with the credentials provided over the web interface?
if yes, does your program uses the exact same credentials? please note that white space can be your enemy.

Sending an Email through gmail SMTP Server (SSL)

I know there's a lot of example on how to send an email using C# but I am really running into some issues and I can't make it to work.
I always get "Failure sending mail" error, Unable to connect to the remote server - No connection could be made because the active machine actively refused it (IP address here).
What does this error mean? And how do I fix this?
Any help will be much appreciated
Here's the code that I've been using: (although I already did try a lot of things)
string SendersAddress = "test#gmail.com";
string ReceiversAddress = "test1#gmail.com";
const string SendersPassword = "test-pass-here";
const string subject = "Testing";
const string body = "Hi This Is my Mail From Gmail";
try
{
SmtpClient smtp = new SmtpClient
{
Host = "smtp.gmail.com",
Port = 587,
EnableSsl = true,
DeliveryMethod = SmtpDeliveryMethod.Network,
Credentials = new NetworkCredential(SendersAddress, SendersPassword),
Timeout = 3000
};
MailMessage message = new MailMessage(SendersAddress, ReceiversAddress, subject, body);
smtp.Send(message);
}
catch (Exception ex)
{
}
Thanks!

It sounds like you're running into issues connecting to the SMTP server.
Make sure the firewall is open on port 25, and that you actually have an SMTP server running wherever you're trying to establish your connection.

You're trying to establish an SSL connection to gmail on port 587. That port must be used with TLS, not SSL.
Use port 465 instead.
Also note that the Timeout property is expressed in milliseconds, so 3000 can be a little short, depending on your network. Try using a more permissive value, like 30000.

Also worth checking that your anti-virus is not blocking port 25, I have been caught by that before!

Same for me in past few days,
Easy solution:
First check if everything is OK with Telnet, then try to do the same in C#.
Here is a good intro : http://www.wikihow.com/Send-Email-Using-Telnet.
Just beware that some servers use the EHLO command instead of HELO
EDIT:
take a look at the way that you can connect to SMTP server of Google here