Cannot send e-mail after reinstalling Thunderbird

For some reason since reinstalling my Thunderbird every time I try to sen e-mail I get the error "Sending of the message failed. An error occurred while sending mail. The mail server responded: <SantoshS1@vbeyond.com>: Recipient address rejected: Access denied. Please check the message recipient "SantoshS1@vbeyond.com" and try again. They are perfectly valid addresses, as they are generated using Reply. This did not happen before I was forced to reinstall from scratch. I suspect it may be some sort of issue with my account configuration in Thunderbird, as I had to recreate that.