为 ASP.NET Core 项目添加电子邮件发送功能，可以使用 Microsoft 提供的 NuGet 包 'Microsoft.AspNetCore.Mvc.Core” 和 'MailKit”。 首先，在项目中安装这两个 NuGet 包：

Install-Package Microsoft.AspNetCore.Mvc.Core
Install-Package MailKit

然后添加以下代码：

using MailKit.Net.Smtp;
using MailKit.Security;
using MimeKit;

public class EmailSender
{
    private readonly string _host;
    private readonly int _port;
    private readonly bool _enableSsl;
    private readonly string _username;
    private readonly string _password;
    private readonly string _from;

    public EmailSender(string host, int port, bool enableSsl, string username, string password, string from)
    {
        _host = host;
        _port = port;
        _enableSsl = enableSsl;
        _username = username;
        _password = password;
        _from = from;
    }

    public async Task SendEmailAsync(string to, string subject, string message)
    {
        var emailMessage = new MimeMessage();
        emailMessage.From.Add(new MailboxAddress("", _from));
        emailMessage.To.Add(new MailboxAddress("", to));
        emailMessage.Subject = subject;
        emailMessage.Body = new TextPart("html")
        {
            Text = message
        };

        using (var client = new SmtpClient())
        {
            await client.ConnectAsync(_host, _port, SecureSocketOptions.StartTls);
            await client.AuthenticateAsync(_username, _password);
            await client.SendAsync(emailMessage);
            await client.DisconnectAsync(true);
        }
    }
}

然后您可以在控制器中使用它：

[ApiController]
[Route("[controller]")]
public class MyController : ControllerBase
{
    private readonly EmailSender _emailSender;

    public MyController(EmailSender emailSender)
    {
        _emailSender = emailSender;
    }

    [HttpPost]
    public async Task Post([FromBody] MyModel model)
    {
        // do something with model

        await _emailSender.SendEmailAsync("recipient@example.com", "Subject line", "Body text");

        return Ok();
    }
}

请注意，此示例需要从配置文件中读取密码和其他敏感信息。您可以使用 ASP.NET Core 的配置系统来实现。