Sending emails to multiple recipients - best practices

Question

My application server needs to notify users about some events via email. Usually there will be between 10-100 users to whom the notifications should be sent, but there may be a few cases where there may be a bit more (I don't think it will ever be more than 1000).

What is the best practice in such cases? Should I send a single email per user or one email with all users as recipients or group users and send one email for each group (for example 1 email for 10 users)? If it makes any difference I may add that I am using System.Net.Mail to send emails.

Thanks in advance for your suggestions

Lukasz Glaz

Answer 1

You should send one e-mail per user.

The alternatives either involve putting e-mails in BCC (which will increase your chances of having your mails flagged as spam), or revealing your user A's e-mail address to user B, where user A and user B are in the same "group".

Answer 2

You need to check with your smtp server manager - to avoid being blocked. if you own the smtp server, than this is not a problem. I think the best way is to send them in bulks of 50 recipients per message (it will be a little faster than one by one).

Answer 3

I wouldn't definetly put all recipients into a To: field. Even from one place. It's just not a good practice to show other's addresses. And it generates a problem when someone hits "Reply All" and suddenly mails all others with his crap :)

If you own the smtp server, and your application server -> smtp server connection isn't slow, I would just send every mail individually, with each single recipient in To: field. It just looks much less spam'ish then getting a mail with empty (or some bogus) To: field and being in BCC only.

Other advantage is the person recieving your mail will know what email address is used. I got plenty of them, use different ones in different places, and it helps to be able to see which one I used on which site (sometimes I need to use this address for password reset / login, and I forgot, and if all mails had me in BCC, I'm screwed). This is from your user's perspective.