返回值
成功并找到邮件：
{"success":true,"status":"success","type":"mail_com","email_type":"mail_com","email":{...},"message":"OK"}
没有邮件：
{"success":true,"status":"empty","type":"mail_com","email_type":"mail_com","email":null,"message":"No emails found"}
请求失败：
{"success":false,"status":"error","type":"mail_com","email_type":"mail_com","email":null,"error":"错误原因","message":"错误原因"}
邮件对象统一包含 id、uid、subject、from、date、timestamp、folder、folder_key、folder_type、body、links 和 source。部分错误会附带 error_code 或 required_email_type。