What methods are there for having .NET code run and handle e-mails as they arrive?

Question

I\'ve been tasked with creating some sort of service that will take any e-mail sent to an e-mail address and handle the contents of the e-mail (including binary attachments.

Answer 1

As with alot of things - it depends. Ask yourself the following questions:

1. What are your latency requirements--do you need to process incoming messages as quickly as possible, or can processing be batched? If it can be batched, then how often would you have to process the "inbox"?

2. What are your throughput requirements? How many messages are we talking about per minute here? How big are the messages? This would affect the decision you make about polling interval if using a batch scenario;

3. What sort of e-mail system are you integrating with? If it's Exchange, what programmatic interfaces are available to access a mailbox? Until the most recent version of Exchange, interestingly enough, there were issues with accessing a mailbox on an Exchange server (The client-side CDO COM components needed to be used which is not ideal---and there were security limitations).

By far the simplest approach is to poll a mailbox using POP3. However, if you need to respond immediately to an incoming message, then this isn't going to cut it.

As far as possible avoid writing your own SMTP service--it's been done a thousand times before and you're just creating unnecessary work for yourself and exposing yourself to security threats. If you absolutely have to respond immediately to messages, then rather set up an instance of Sendmail or Postfix to spawn a process that you have written.

If you're going to go for the POP3 solution (it looks like you are), then have a read of related questions "Free POP3 .NET library?" and "Reading Email using POP3 in C#".