MultiplesEmails.cs

using System.Net.Mail;
MyEmailBatch myEmailBatch = new MyEmailBatch
{
    Message = "Hello this is a general shared message",
    Sender = "name@email.com",
    Recipients = new[] { "name1@email.com", "name2@email.com", "name3@email.com" },
    SenderName = "Me"
};



MailAddress sender = new MailAddress(myEmailBatch.Sender, myEmailBatch.SenderName);
System.Net.Mail.SmtpClient client;
var requests = myEmailBatch.Recipients.Select(async x => {
    MailAddress to = new MailAddress(x);
    using (MailMessage message = new MailMessage(sender, to))
    {
        message.Subject = myEmailBatch.Subject;
        message.Body = myEmailBatch.Message;
        using (client = new System.Net.Mail.SmtpClient
        {
            Host = "smtp.gmail.com",
            Port = 587,
            EnableSsl = true,
            UseDefaultCredentials = false,
            Credentials = new System.Net.NetworkCredential(myEmailBatch.Sender, "password")
        })
        {
            await client.SendMailAsync(message);
        }
    }
    Thread.Sleep(1000);

});

await Task.WhenAll(requests);

MailAddress from = new MailAddress(myEmailBatch.Sender, myEmailBatch.SenderName);
MailAddress to = new MailAddress(myEmailBatch.Recipients[0]);
MailMessage message = new MailMessage(from, to);
message.Subject = "Subject";
string body = "Body";
message.Body = body;
myEmailBatch.Recipients.Select(x =>
{
    message.Bcc.Add(new MailAddress(x));
    return true;
});
using (client = new System.Net.Mail.SmtpClient
{
    Host = "smtp.gmail.com",
    Port = 587,
    EnableSsl = true,
    UseDefaultCredentials = false,
    Credentials = new System.Net.NetworkCredential(myEmailBatch.Sender, "password")
})
{
    await client.SendMailAsync(message);
}

class MyEmailBatch
{
    public string Message { get; set; }
    public string Sender { get; set; }
    public string SenderName { get; set; }
    public string Subject { get; set; }
    public IList<string> Recipients { get; set; }
};

class EmailSenderStream
{
    MyEmailBatch myEmailBatch = new MyEmailBatch
    {
        Message = "Hello this is a general shared message",
        Sender = "name@email.com",
        Recipients = new[] { "name1@email.com", "name2@email.com", "name3@email.com" },
        SenderName = "Me"
    };
    public async IAsyncEnumerable<string> GetEmails()
    {
        foreach (var recipients in myEmailBatch.Recipients.Select(x => x))
        {
            yield return recipients;
        }
    }
    public async Task SendEmail()
    {
        await foreach (var recipient in GetEmails())
        {
            MailAddress to = new MailAddress(recipient); 
            MailAddress from = new MailAddress(myEmailBatch.Sender);
            using (MailMessage message = new MailMessage(from, to))
            {
                message.Subject = myEmailBatch.Subject;
                message.Body = myEmailBatch.Message;
                using (var client = new System.Net.Mail.SmtpClient
                {
                    Host = "smtp.gmail.com",
                    Port = 587,
                    EnableSsl = true,
                    UseDefaultCredentials = false,
                    Credentials = new System.Net.NetworkCredential(myEmailBatch.Sender, "password")
                })
                {
                    await client.SendMailAsync(message);
                }
            }
        }
    }

}