How to handle mass email alert system for a registered userbase

Question

I have a client who would like a system developed which handles sending out alert emails to opted-in registered users. The alerts are based on geographic travel-related incidents and these are provided via a third party web service. The registered userbase is expected to be around 500,000 users and each user can subscribe to multiple alert categories.

I'm just trying to scope out what would be required technically to create this alerting functionality. In my mind we would create something like the following:

• Poll the alert service once hourly
• Store a "queue" of alerts in a temporary database table
• Process the queue table as a scheduled task and send out the emails to the opted-in users

The part that I'm really not sure about is the physical sending of the emails. I was wondering if anyone could recommend any good options here. I guess we're looking to either create a custom component to send out the emails or use a dedicated third party service (like dotMailer maybe? Or a custom mass mail server?). I've read that rolling out your own solution runs the risk of having IP's blacklisted if you're not careful, and obviously we want to keep this all completely legitimate.

I should also mention that we will be looking to create the solution using .NET (C#) and we're limited to SQL Server Express 2008 edition.

Any thoughts much appreciated

Many thanks in advance

Answer 1

For the Poll , Queue and Send operations I'd create a windows service that calls the external service , operates on the data and then gathers the results to send out the emails updating the database as necessary with sent flags etc.

I handled a similar project recently and we found many ISPs or Hosting Providers got really twitchy when we mentioned mass emails. You should defintly check out the http://en.wikipedia.org/wiki/CAN-SPAM_Act_of_2003 CAN SPAM guidelines (or similar in your territory).

As long as you play by the rules and follow the guidelines you should be OK sending out from a local mail server however its important that you ensure that DNS Lookups or Reverse DNS lookups on the MX records all point back and forth to each other properly. Indeed this would be easier to out source to a third party mail provider or ISV but when we tried we were unable to find a good fit and ended up doing it ourselves.

Additionally you may want to glance at SPF records and other means to increase mass email delivery! For what its worth this can be a very tricky task to implement as SMTP (my least favourite protocol) is painful to try to debug and people get very upset if they receive multiples or unsolicited emails so ensure you have an Opt-in policy and appropriate checks to prevent duplicate delivery.