Gmail flagging my C# SMTP emails as suspicious

Other Questions Gmail
1

I’m having trouble with my C# program that sends emails through Gmail’s SMTP server. The emails are being flagged as suspicious by Gmail on the receiving end. It shows a warning saying the message might not be from the sender’s address.

I’m using a Gmail address as the sender. Here’s a simplified version of my code:

public class EmailSender
{
    public string From { get; set; }
    public string To { get; set; }
    public string Topic { get; set; }
    public string MessageBody { get; set; }
    private string Secret { get; set; }

    public void Dispatch()
    {
        var mail = new MailMessage(From, To)
        {
            IsBodyHtml = true,
            Subject = Topic,
            Body = MessageBody
        };

        using (mail)
        {
            CreateSmtpClient(From, Secret).Send(mail);
        }
    }

    private static SmtpClient CreateSmtpClient(string user, string pass)
    {
        return new SmtpClient
        {
            Host = "smtp.gmail.com",
            Port = 587,
            EnableSsl = true,
            DeliveryMethod = SmtpDeliveryMethod.Network,
            UseDefaultCredentials = false,
            Credentials = new NetworkCredential(user, pass)
        };
    }
}

Can anyone spot what might be causing this issue? I’m confused about why Gmail is marking these emails as potential phishing attempts.

2

I’ve been down this road before, and it can be frustrating. One thing that worked for me was implementing DKIM (DomainKeys Identified Mail) and SPF (Sender Policy Framework) records. These authentication methods help verify that your emails are legitimate and coming from an authorized source.

To set this up, you’ll need access to your domain’s DNS settings. Add the appropriate SPF and DKIM records as provided by Google. This can significantly improve your email deliverability and reduce the chances of being flagged as suspicious.

Also, consider gradually ramping up your email sending volume. Starting with a low volume and slowly increasing it over time can help build a positive sender reputation with Gmail. It takes some patience, but it’s worth it in the long run for maintaining a good email sending reputation.

3

I’ve encountered this issue before when sending emails programmatically through Gmail’s SMTP server. The problem likely stems from Gmail’s strict security measures to prevent unauthorized use of their servers for sending emails.

To resolve this, you need to enable ‘Less secure app access’ in your Google Account settings. However, Google has deprecated this option for security reasons. Instead, I recommend using OAuth 2.0 for authentication. This involves creating a Google Cloud project, setting up OAuth consent, and generating the necessary credentials.

Alternatively, you could use Google’s API client library for .NET, which simplifies the OAuth process. This approach is more secure and aligns with Google’s current best practices for email sending.

Remember to also verify your domain if you’re sending from a custom domain, as this can help improve deliverability and reduce the likelihood of your emails being flagged as suspicious.

4

hey there! i’ve dealt with this too. Gmail’s gotten real picky lately. Have u tried using app passwords instead? It’s easier than oauth and works great. Just go to ur google account, make an app password, and use that in ur code. should fix the issue :slight_smile: