Email delivery issues with Gmail SMTP in C#

Other Questions Gmail
1

I’m working on an email application for my university assignment. The SMTP functionality works great with most email providers, but I keep running into problems when trying to connect to Gmail’s servers. I think the issue might be related to SSL certificate validation, but I’m not completely sure.

Here’s my current setup:

EmailSender sender = new EmailSender("smtp.gmail.com", 587);
sender.EnableSsl = true;
sender.UseDefaultCredentials = false;
sender.Credentials = new NetworkCredential("myuser", "mypass");

try
{
    EmailMessage msg = new EmailMessage();
    msg.To.Add("[email protected]");
    msg.From = new MailAddress("[email protected]");
    msg.Subject = "Testing email";
    msg.Body = "This is a test message";
    
    sender.Send(msg);
    msg = null;
}
catch (Exception ex)
{
    Console.WriteLine("Failed to send email: " + ex);
}

The error I get mentions SSL authentication problems and certificate chain issues. Has anyone encountered similar problems when integrating with Gmail’s SMTP service?

2

Had this exact problem building an automated reporting tool for accounting. It’s definitely auth-related. Google killed less secure app access, so regular passwords don’t work anymore. You need to turn on two-factor auth first, then create an app password in Google Account Security settings. Use that 16-character app password in NetworkCredential instead of your regular one. Also check if your custom EmailSender class is messing with TLS negotiation. Gmail needs TLS 1.2 minimum and some wrapper implementations screw up the protocol version.

3

check ur port settings - gmail smtp uses 587 with starttls, but switching to port 465 might fix cert errors. idk if ur custom classes deal w/ ssl handshake as well as SmtpClient. try out basic SmtpClient first to find out if it’s ur wrapper code or gmail auth that’s the prob.

4

Had the exact same SSL certificate chain error building an email notification system last year. In my case, it was Gmail’s stricter certificate validation plus using regular passwords instead of app passwords. You need to generate an app-specific password from your Google Account settings - don’t use your regular Gmail password. Also noticed you’re using custom EmailSender and EmailMessage classes. If those wrap around SmtpClient, make sure they handle certificate validation callbacks properly. Sometimes adding ServerCertificateValidationCallback helped me debug the specific certificate issues. Gmail’s SSL handshake gets finicky when certificate chain validation isn’t handled right in wrapper classes.