I'm convinced that all e-mail solutions are flawed. Based on experience.
One option is to do a thorough housecleaning on your computer (its best to have this done by professionals - I've been happy with Staples, unhappy with Geek Squad). That will entail reinstalling the operating system and Office, and that may fix your problem.
If not, then you need to look for an alternate. Thunderbird is now known as Eudora OCE and is a free download. It works well, but the interface is not the same as Outlook Express so you have to learn something new. It is possible to migrate from Outlook or Outlook Express to Eudora, but my experience is that migration in the reverse direction does not always work.
Another option is to switch to one of the free webmail services. The best is Gmail (a Google product). You access it via your browser (it works with any browser, but the interface with Chrome is seamless), and you can also access it using a mobile device.