这只是一个例子：

*:** (BC hrs) --> May ??: ? pm

On Tue, May ??, 2026 at ?:?? Mail Delivery Subsystem <mailer-daemon@googlemail.com> wrote:

Delivery incomplete

There was a temporary problem delivering your message to ******@math.????.edu.cn. Gmail will retry for BC more hours. You'll be notified if the delivery fails permanently.