<p>I'm currently looping through a datareader and calling the System.Net.Mail.SmtpClient's Send() method. The problem with this is that it's slow. Each email takes about 5-10 seconds to send (it's possible this is just an issue with my host). I had to override the executionTimeout default in my web.config file (it defaults to 90 seconds) like this:</p>

<pre><code> &lt;httpRuntime executionTimeout="3000" /&gt;
</code></pre>

<p>One caveat: I'm on a shared host, so I don't think it is possible for me to send using the PickupDirectoryFromIis option (at least, it gave me errors when I turned it on).</p>

You could send the mail asynchronous. That way the timeout should not interrupt your sending.
This article should help you get started with that:
Sending Emails Asynchronously in C#
.
There is another approach here:
http://www.vikramlakhotia.com/Sending_Email_asynchronously_in_AspNet_20.aspx
And off course there are several commercial clients available, but the only one that i have tried and can recommend is
http://www.aspnetemail.com/