Send thousands of emails at a time, pitfalls/best way?

Question

Im writing a tool c# (and System.Net.Mail) which will be sending around 4000 emails fornigtly.

Can i simply loop through a list of 4000 email addresses and send emails one at a time? or will this cause any potential problems?

Is there a better way to do this?

Thanks

Answer 1

First of all you must have rDNS record that will map IP address back to domain name. Without it mail services like GMail will hold your e-mails for hours or even days. Furthermore you may become blacklisted after few dozens of letters. rDNS usually can be set using hoster's control panel or by support request.

Second, don't be tempted to use your ISP's or GMail's SMTP servers. You will quickly run out of daily quota. It is usually not allowed to send more than few dozens letters (50 for GMail AFAIK). So either send mail from your own server, or use a 3rd party service like auth smtp.

Such services are useful also if you're unable to set rDNS for some reason.

P.S. If the content of your letters is OK (i.e. they are not spam actually) and rDNS/SMTP are set correctly, you can send at any rate, without pauses.

Answer 2

Provided you don;t break any server limitations, such as memory or disk space, technically there is no issue. However you will run into problems with with ISP's and mail forwarders who may block your domains for spam - rightly or wrongly..