.net how - Sending email through Gmail SMTP server with C#

secure asp (23)

For some reason neither the accepted answer nor any others work for me for "Sending email in .NET through Gmail". Why would they not work?

UPDATE: I have tried all the answers (accepted and otherwise) in the other question, but none of them work.

I would just like to know if it works for anyone else, otherwise Google may have changed something (which has happened before).

When I try the piece of code that uses SmtpDeliveryMethod.Network, I quickly receive an SmtpException on Send(message). The message is

The SMTP server requires a secure connection or the client was not authenticated.

The server response was:

5.5.1 Authentication Required. Learn more at" <-- seriously, it ends there.


This is a question that I asked a long time ago, and the accepted answer is code that I've used many, many times on different projects.

I've taken some of the ideas in this post and other EmailSender projects to create an EmailSender project at Codeplex. It's designed for testability and supports my favourite SMTP services such as GoDaddy and Gmail.


Turn On Access For Less Secure Apps and it will work for all no need to change password.

Link to Gmail Setting

In addition to the other troubleshooting steps above, I would also like to add that if you have enabled two-factor authentication (also known as two-step verification) on your GMail account, you must generate an application-specific password and use that newly generated password to authenticate via SMTP.

To create one, visit: https://www.google.com/settings/ and choose Authorizing applications & sites to generate the password.

I ran into this same error ( "The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at" ) and found out that I was using the wrong password. I fixed the login credentials, and it sent correctly.

I know this is late, but maybe this will help someone else.

Another thing that I've found is that you must change your password at least once. And try to use a secure level password (do not use the same user as password, 123456, etc.)

  smtp.Host = "smtp.gmail.com"; //host name
    smtp.Port = 587; //port number
    smtp.EnableSsl = true; //whether your smtp server requires SSL
    smtp.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
    smtp.Credentials = new NetworkCredential(fromAddress, fromPassword);
    smtp.Timeout = 20000;

I was using corporate VPN connection. It was the reason why I couldn't send email from my application. It works if I disconnect from VPN.


I got the exact same error, it turns out Google's new password strengh measuring algorithm has changed deeming my current password as too weak, and not telling me a thing about it (not even a message or warning)... How did I discover this? Well, I chose to change my password to see if it would help (tried everything else to no avail) and when I changed my password, it worked!

Then, for an experiment, I tried changing my password back to my previous password to see what would happen, and Gmail didn't actually allow me to do this, citing the reason "sorry we cannot allow you to save this change as your chosen password is too weak" and wouldn't let me go back to my old password. I figured from this that it was erroring out because either a) you need to change your password once every x amount of months or b). as I said before, their password strength algorithms changed and therefore the weak password i had was not accepted, even though they did not say anything about this when trying to login ANYWHERE! This (number 2) is the most likely scenario, as my weak password was about 4 months old, and it let me use it in Gmail.

It's pretty bad that they said nothing about this, but it makes sense. Because most hijacked emails are logged into using software outside of gmail, and I'm guessing you are required to have a stronger password if you want to use Gmail outside of the Gmail environment.

I hope this helps!

I was getting the same error and none of the above solutions helped.

My problem was that I was running the code from a remote server, which had never been used to log into the gmail account.

I opened a browser on the remote server and logged into gmail from there. It asked a security question to verify it was me since this was a new location. After doing the security check I was able to authenticate through code.

I also found that the account I used to log in was de-activated by google for some reason. Once I reset my password (to the same as it used to be), then I was able to send emails just fine. I was getting 5.5.1 message also.

The problem is not one of technical ability to send through gmail. That works for most situations. If you can't get a machine to send, it is usually due to the machine not having been authenticated with a human at the controls at least once.

The problem that most users face is that Google decides to change the outbound limits all the time. You should always add defensive code to your solution. If you start seeing errors, step off your send speed and just stop sending for a while. If you keep trying to send Google will sometimes add extra time to your delay period before you can send again.

What I have done in my current system is to send with a 1.5 second delay between each message. Then if I get any errors, stop for 5 minutes and then start again. This usually works and will allow you to send up to the limits of the account (last I checked it was 2,000 for premier customer logins per day).

One or more reasons are there for these error.

  • Log in with your Gmail( or any other if ) in your local system.

  • Also check for Less Secure App and Set it to "Turn On" here is the Link for GMAIL. https://www.google.com/settings/security/lesssecureapps

  • check for EnableSsl in your Email code, and also set it to true.

    smtp.EnableSsl = true;
  • Also check which port are you using currently. 25 is Global, but you can check it for others too like 587. check here. Does all SMTP communication happen over 25?

  • IF YOU ARE ON REMOTE : Check the answer of Vlad Tamas above.

@Andres Pompiglio: Yes that's right you must change your password at least once.. this codes works just fine:

//Satrt Send Email Function
public string SendMail(string toList, string from, string ccList,
    string subject, string body)

    MailMessage message = new MailMessage();
    SmtpClient smtpClient = new SmtpClient();
    string msg = string.Empty;
        MailAddress fromAddress = new MailAddress(from);
        message.From = fromAddress;
        if (ccList != null && ccList != string.Empty)
        message.Subject = subject;
        message.IsBodyHtml = true;
        message.Body = body;
        // We use gmail as our smtp client
        smtpClient.Host = "smtp.gmail.com";   
        smtpClient.Port = 587;
        smtpClient.EnableSsl = true;
        smtpClient.UseDefaultCredentials = true;
        smtpClient.Credentials = new System.Net.NetworkCredential(
            "Your Gmail User Name", "Your Gmail Password");

        msg = "Successful<BR>";
    catch (Exception ex)
        msg = ex.Message;
    return msg;
//End Send Email Function

AND you can make a call to the function by using:

Response.Write(SendMail(recipient Address, "[email protected]", "ccList if any", "subject", "body"))

Change your gmail password and try again, it should work after that.

Don't know why, but every time you change your hosting you have to change your password.

Oh...It's amazing... First I Couldn't send an email for any reasons. But after I changed the sequence of these two lines as below, it works perfectly.

client.UseDefaultCredentials = true;
client.Credentials = new System.Net.NetworkCredential("[email protected]", "password");

Hope this help!!! :)

  1. First check your gmail account setting & turn On from "Access for less secure apps"

We strongly recommend that you use a secure app, like Gmail, to access your account. All apps made by Google meet these security standards. Using a less secure app, on the other hand, could leave your account vulnerable. Learn more.

  1. Set

    smtp.UseDefaultCredentials = false;


    smtp.Credentials = new NetworkCredential(fromAddress, fromPassword);

I had the same problem, but it turned out to be my virus protection was blocking outgoing "spam" email. Turning this off allowed me to use port 587 to send SMTP email via GMail

I had also try to many solution but make some changes it will work

host = smtp.gmail.com
port = 587
username = [email protected]
password = password
enabledssl = true

with smtpclient above parameters are work in gmail

I had this problem resolved. Aparently that message is used in multiple error types. My problem was that i had reached my maximum of 500 sent mails.

log into the account and manually try to send a mail. If the limit has been reached it will inform you

Yet another possible solution for you. I was having similar problems connecting to gmail via IMAP. After trying all the solutions that I came across that you will read about here and elsewhere on SO (eg. enable IMAP, enable less secure access to your mail, using https://accounts.google.com/b/0/displayunlockcaptcha and so on), I actually set up a new gmail account once more.

In my original test, the first gmail account I had created, I had connected to my main gmail account. This resulted in erratic behaviour where the wrong account was being referenced by google. For example, running https://accounts.google.com/b/0/displayunlockcaptcha opened up my main account rather than the one I had created for the purpose.

So when I created a new account and did not connect it to my main account, after following all the appropriate steps as above, I found that it worked fine!

I haven't yet confirmed this (ie. reproduced), but it apparently did it for me...hope it helps.

I'm not sure which .NET version is required for this because eglasius mentioned there is no matching enableSsl setting (I'm using .NET 4.0, but I suspect it to work in .NET 2.0 or later), but this configuration justed worked for me (and doesn't require you to use any programmatic configuration):

    <smtp from="[email protected]" deliveryMethod="Network">
      <network defaultCredentials="false" enableSsl="true" host="smtp.gmail.com" port="587" password="password" userName="[email protected]"/>

You might have to enable POP or IMAP on your Gmail account first: https://mail.google.com/mail/?shva=1#settings/fwdandpop

I recommend trying it with a normal mail client first...

You can find it here: http://jayrambhia.com/blog/send-emails-using-python

smtp_host = 'smtp.gmail.com'
smtp_port = 587
server = smtplib.SMTP()
fromaddr = raw_input('Send mail by the name of: ')
tolist = raw_input('To: ').split()
sub = raw_input('Subject: ')

msg = email.MIMEMultipart.MIMEMultipart()
msg['From'] = fromaddr
msg['To'] = email.Utils.COMMASPACE.join(tolist)
msg['Subject'] = sub  
msg.attach(MIMEText(raw_input('Body: ')))
msg.attach(MIMEText('\nsent via python', 'plain'))

c# .net email smtp gmail