一等邮件：指邮政系统中的最高级别邮件，通常具有较快的投递速度和更高的优先级。
mail that includes letters and postcards and packages sealed against inspection
同义词： first class / 1st class / 1st-class mail
First-Class Mail（普通邮件）是快速且实惠的服务，适用于重量在 13 盎司以内的信封和包裹。可以在 3 天之内或更少天数内投递。
一等国际邮递(First-class Mail),没有邮递时间的保证,以盎司为单位计价.(OUNCE),每次最多可寄 64 OUNCES = 4 LB
... 优先邮件(Priority Mail): 一类邮件(First-Class Mail): 包裹(Parcel Post): ...
_百度知道已解决 · 上次更新日期: 2007/7/29 · 6 条答复最佳答案 · First-Class Mail (普通信件) First Class Mail (1-3 day ) 这种一般都是算 first class mail 重量不能超过 13 盎司 .
And it gets worse.By 2020, first-class mail volume is expected to drop by half.
2020年的情况会更糟，一类邮件数量预计将减少一半。
And it gets worse. By 2020, first-class mail volume is expected to drop by half.
2020年的情况会更糟，一类邮件数量预计将减少一半。
It arrived by first-class mail in second-class condition. It is impossible to tell where the law stops and justice begins.
头等邮件收到时却是二等情况。你无法说得准在何处法律让位给正义。
That wasn't nearly enough to make up for a 3.1% decline in first-class mail, still the main revenue driver.
The Postal Service said it would end Saturday first-class mail delivery beginning Aug. 5 in an effort to curb losses.
The U.S. Postal Service is moving forward with plans to make cuts to its first-class mail next spring, as it shutters about half of its 487 mail processing centers.