I suspect that the culprit for these repeated 103 errors is the Microsoft DNS Client service.

For whatever reason, it is not keeping it's cache up to date. I've had a DNS lookup attempted until I believed that it would never be resolved.

So I turned the DNS Client service off, and disabled it.

Since doing this, all of my URLs are still resolved by my ISPs DNS (maybe even faster) in Internet Explorer, and SpamX is resolving names. It may have to retry once in a while, but it always seems to get an answer. This was not the case before.

To disable this service on your computer, go to Control Panel, click Administrative Tools, click Services.

Right click on DNS Client, and click Stop.
Right click on DNS Client, and click Properties, then in Startup type: select Disabled, the click Ok.

I'm curious if you have the same experience...

By golly you may be on to something. I did as you suggested and disabled DNS CLient service. I only had three spams this morning, but they all went through in nearly no time. We'll know better how well this works when I have some more of the hated stuff to process.
BTW, I did this with v. 2.2.2 because I haven't had the socket 103 error for some time now, at least 2 revisions ago. I didn't want to fix somethong that wasn't broke.

Great Codger! You might want to download the executable for 2.2.3 anyway. As I make changes to the code it is also groomed with the idea of making it better, so some minor changes were made to the code in general...

Won't turning off the DNS client mess up internet connection sharing?

Good question, I could be wrong, but I don't think so.

My understanding is, that the DNS Client is only responsible for (poorly ) maintaining the cache for DNS, and Active Directory.

There's one way to find out, and it's painless to undo...