SMTP Outlook can't send Emails

Question

i'm stuck in this problem when button click it always says "Failure to send email" I try several host like smtp.office365.com, pod51015.outlook.com and ports like 465, 25 and nothing seems to work

                string _sender = "myEmail.com";
                string _password = "myPass";

                SmtpClient client = new SmtpClient("smtp-mail.outlook.com");

                client.Port = 587;
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.UseDefaultCredentials = false;
                System.Net.NetworkCredential credentials =
                    new System.Net.NetworkCredential(_sender, _password);
                client.EnableSsl = true;
                client.Credentials = credentials;

                MailMessage message = new MailMessage(_sender, "toEmail.com");
                message.Subject = "mySubject";
                message.Body = "myBody";
                client.Send(message);

CTTO of this code which I also found in this forum which seem they worked for them.

take a look at : https://stackoverflow.com/questions/704636/sending-email-through-gmail-smtp-server-with-c-sharp — jazb, Apr 01 '22 at 03:36
if I use Gmail SMTP it works just this outlook catching error @Jazb — Byte, Apr 01 '22 at 04:32
if i use Gmail SMTP and Gmail account it works fine while in outlook I get error — Byte, Apr 01 '22 at 04:42
Does this answer your question? [Sending email through Gmail SMTP server with C#](https://stackoverflow.com/questions/704636/sending-email-through-gmail-smtp-server-with-c-sharp) — Eugene Astafiev, Apr 03 '22 at 22:00

score 1 · Answer 1 · answered Apr 01 '22 at 23:36

1

Your code looks like mine, except I did force .NET to use TLS 1.2. TLS 1.1 was deprecated by office365.com in January, and this caused problems with my application.

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;

answered Apr 01 '22 at 23:36

A. Niese

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score 0 · Answer 2 · answered Apr 01 '22 at 04:21

0

Office 365 SMTP servers no longer allow Basic auth by default - see https://learn.microsoft.com/en-us/exchange/clients-and-mobile-in-exchange-online/deprecation-of-basic-authentication-exchange-online

answered Apr 01 '22 at 04:21

Dmitry Streblechenko

62,942
4
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what should be the workaround – Byte Apr 01 '22 at 05:12
You need to either re-enable Basic auth for your tenant or use OAuth2 for the SMTP connection. – Dmitry Streblechenko Apr 01 '22 at 05:14

score 0 · Answer 3 · answered Apr 06 '22 at 06:44

0

Let's try this workaround, it could be helpful.

Enable Legacy TLS: Set-TransportConfig -AllowLegacyTLSClients $true
Confirm Legacy TLS is set: Get-TransportConfig | Format-List AllowLegacyTLSClients

Change the SMTP endpoint to smtp-legacy.office365.com

answered Apr 06 '22 at 06:44

Ratul

43
2
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How-to use ***AllowLegacyTLSClients*** in NET (C#) with a SmtpClient class? – Kiquenet Jun 17 '22 at 19:31
You have to enable the Legacy TLS on your Microsoft Exchange Admin first. Then use _smtp-legacy.office365.com_ as _HOST_ – Ratul Jun 23 '22 at 17:10

SMTP Outlook can't send Emails

3 Answers3