Typically it will be a monotonically increasing value starting from a random seed, but the client is free to use whatever request IDs it likes.
一般它会是一个从随机基数开始的递增值，不过客户端想用什么样的请求ID都可以。
The -bv flag will start Sendmail with a request to verify the user IDs provided in the Address parameter field of the command.
—bv标志启动Sendmail并请求确认命令的Address参数字段中指定的用户ID。
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