Why does IISReset or AppPool Recycling won't refresh my email receiver code?
For those who are working on event receivers to enable incoming email for custom list, or out of the box lists that do not have incoming email feature, when you deploy new assemblies, you are probably recycling your app pool, or hitting IISReset, and test your new code. But during testing, you may find that your code doesn't refresh. The reason is because the web application does not monitor and process emails, but SharePoint timer job does that. Hence to get your code refreshed, you have to go to services, and restart Windows SharePoint Services Timer service.