So that the CRDMail server is not used as a spam portal, you are permitted to send only 60-100 emails an hour. If you attempt to send any more, your account is blocked until the hour is up.
Here's what to do: Make sure that you are using the very latest build of CRD. In Options, check "Try resending failed mails".
When you go over the hourly quota, CRD will keep retrying and the mails will be sent as soon as your account has been restored.
Oh yeah. I knew that! I guess I should also adjust schedule times, where possible, in order to "spread the wealth" out across a broader period of time. Thanks for the response!