CODEWITHSUNDEEP
c#asynchronousasync-awaitsmtpclient
thanhnguyen.1701
thanhnguyen.1701

Reputation: 45

SMTP send multiple mail by adding multiple to vs Async method

Question : I have a list of 50~100 person i need send email to, MailMessage allows me to add a list of To(MailAddressCollection) and just smtpClient.Send(mail) or the Async method ? What is the best practice for sending email to multiple recipients ?

Upvotes: 1

Views: 1890

Answers (2)

Kevin Brydon
Kevin Brydon

Reputation: 13112

From what I understand from your question, you're currently trying to decide which of these is better?

Adding all emails to a single MailMessage and send syncronously

var mailAddressCollection = new MailAddressCollection();
mailAddressCollection.Add("[email protected],[email protected]...");
// initialize the message and smtpclient
smtpClient.Send(message);

This will result in a single email being sent. All recipients will be able to see who the email went to. Depending on application, it might be a breach of privacy if sending to customers. Send will block the calling thread.

Adding all emails to a single MailMessage and send asyncronously

var mailAddressCollection = new MailAddressCollection();
mailAddressCollection.Add("[email protected],[email protected]...");
// initialize the message and smtpclient
await smtpClient.SendMailAsync(message);

Same as above except SendMailAsync will not block the calling thread.

Create a new MailMessage for each email address and send syncronously

// emailAddresses is a collection of strings
var mailAddressCollection = new MailAddressCollection();
foreach (var emailAddress in emailAddresses)
{
    // initialize the message and smtpclient
    smtpClient.Send(message);
}

This will result in one email being sent for each email address. The recipients will not know who else got the same email as they will be the only address if the "To" field. Because an individual email is being sent for each email address, the time to complete the loop is proportional to the number of email addresses. E.g. if it takes 2 seconds to send 1 email, it will take 200 seconds to send 100 emails.

Create a new MailMessage for each email address and send asyncronously

// emailAddresses is a collection of strings
var mailAddressCollection = new MailAddressCollection();
foreach (var emailAddress in emailAddresses)
{
    // initialize the message and smtpclient
    await smtpClient.SendMailAsync(message);
}

Same as above except SendMailAsync will not block the calling thread.

A note on using SmtpClient

Microsoft do not recommend using SmtpClient for new development as it doesn't support modern protocols. They currently recommend using MailKit or other libraries. Personally, I haven't used SmtpClient in years, instead delegating all my email sending to third parties such as MailGun and SendGrid.

See https://github.com/dotnet/platform-compat/blob/master/docs/DE0005.md

Upvotes: 2

Johnathan Barclay
Johnathan Barclay

Reputation: 20373

Rather than serialise the email sending, you can dispatch the send requests in parallel then wait for them all to finish sending.

IEnumerable<MailMessage> emails = // create your email collection
var sendTasks = emails.Select(smtpClient.SendMailAsync);
await Task.WhenAll(sendTasks);

This will be more efficient when there is a large number of emails to send.

Upvotes: 2

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