That message indicates your Internet Service Provider uses an SMTP protocol that BigOven doesn't currently support.
A workaround is to highlight the recipe(s) you'd like to send in an email in the results list, then use "Copy Recipe Text" from the Edit menu to copy recipes to the Clipboard, then paste them into your favorite email client. (You can also post the recipes to BigOven.com and email from there.) We've got more robust support for other email protocols on the enhancement list for future versions of the software. Thanks!