I'm sorry to hear you've had trouble with the test sends for your email, but I can provide some insight into what's happening.
As a means of preventing spam and billing mitigation, we only allow up to 50 test sends to non-verified email addresses in a 24-hour period. The email address you most frequently sent to during this time is not verified in your account. If there is a particular email address that you know you'll be test sending to a lot, you may want to add them as a verified address.
If you have any other questions or concerns, feel free to reply to this thread or create a new one, and we'd be happy to assist.
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