Cannot send mail with c#

Question

Have this c# code and trying to send mail:

            MailMessage mail = new MailMessage(fromAddress.Address, toAddress.Address);  
            SmtpClient client = new SmtpClient();  

            client.EnableSsl = true;  
            client.Host = "smtp-mail.outlook.com";  
            client.UseDefaultCredentials = false;  
            client.Credentials = new NetworkCredential(fromAddress.Address,   
                fromPassword);  
            client.Port = 587;  
            client.DeliveryMethod = SmtpDeliveryMethod.Network;  
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls |  
                SecurityProtocolType.Tls11 | SecurityProtocolType.Tls12;  

            mail.Subject = subject;  
            mail.Body = body;  

            client.Send(mail);  

Get the error message: Client not authenticated to send mail. Error: 535 5.7.139 Authentication unsuccessful, the user credentials were incorrect

What do I have to do?

Answer 1

Hi again Dillon

Do not understand what's happening, it works when I debug the code but not when I run it. I get the error: 5.7.0 Authentication Required.

Best regards
Göran

Answer 2

Hi @Göran Härdelin

It looks like you need to conform to what Office 365 wants:

https://stackoverflow.com/questions/30342884/5-7-57-smtp-client-was-not-authenticated-to-send-anonymous-mail-during-mail-fr

Try changing your server to smtp.office365.com

https://learn.microsoft.com/en-us/exchange/mail-flow-best-practices/how-to-set-up-a-multifunction-device-or-application-to-send-email-using-microsoft-365-or-office-365#how-to-set-up-smtp-auth-client-submission

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If this is helpful please accept answer.

Answer 3

Hi again Dillon

I don't have an office365 email, just an outlook email. Get the same error as before, but in debug mode it's working. Don't understand why it's working in debug but not in production.

Best regards
Göran