Sending different body via Amazon SES Api - asp.net-mvc

Question

I am using Amazon-SES api for sending email to clients. It's very successfull but i have to send different body for each client. When i start to send mails about 200.000 clients, how the code below look like ? Is it loop 200.000 times or can i prepare an object and send one time (like n:n system, now it's 1:n).
var clientList=new List<String>(); //200.000 mail adress
foreach(var to in clientList)
{
SendEmailRequest email = new SendEmailRequest();
email.Message = new Message();
email.Message.Body = new Body();
email.Message.Body.Html = new Content(bodyhtml);
email.Message.Subject = new Content(subject);
email.WithDestination(new Destination() { ToAddresses = new List<String>() { to } })
.WithSource("mysite#mysite.com")
.WithReturnPath("mysite#mysite.com");
SendEmailResponse resp = client.SendEmail(email); //that's 1:n
}
SendEmailResponse resp = client.SendEmail(emailList); //that's n:n but it's a wrong usage
How can i send n:n algorithm in Amazon SES ?
Application is Asp.net MVC 3. So can i use Asynchronous Controller ? Is it good idea ?

Answer 1

Assuming you have production access for Amazon SES already (see What should I do after I'm finished testing and evaluating Amazon SES?) and a sufficiently increased Sending Quota to send 200.000 mails/day in the first place (see How Amazon SES Sets Sending Limits), the respective limits are documented for the SendEmail action:
The total size of the message cannot exceed 10 MB.
Amazon SES has a limit on the total number of recipients per message:
The combined number of To:, CC: and BCC: email addresses cannot exceed
50. If you need to send an email message to a larger audience, you can divide your recipient list into groups of 50 or fewer, and then call
Amazon SES repeatedly to send the message to each group. [emphasis mine]
Please note: It is strictly recommended to use Bcc: only for this kind of mass mailing operation, else your users will see their mail addresses exposed to each other and I can guarantee they won't be amused at all!
So you could prepare mails with 50 Bcc: recipients at a time, dropping the outbound mail amount for your use case to about 4.000, which is a considerable improvement already. However, please note a respective AWS Team response to Increase sending limit, and question on FAQ:
if you're sending to multiple ISPs [...], I would recommend
sending to one address at a time since certain ISPs are sensitive
about multiple addresses on the BCC: line in large quantities. [emphasis mine]
Whether or not this warning applies depends on your use case as usual (e.g. you might be able to shard the mails by ISP etc.).
Doing it asynchronously is fine and likely useful, but you need to ensure to stay within your Maximum Send Rate (mails/second) limit as well. These limits are visible in the SES tab of the AWS Management Console, but available via the API as well of course (see Monitoring Your Sending Limits for details).