Assume that a certain mail volume (in GB) has to be archived per day.

假设每天要归档一定量(以gb计)的邮件。

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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。

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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。

youdao

The cut in staff comes as the volume of mail in the United States is declining.

VOA: standard.2010.04.13

As mail volume increased, the Postal Service asked charitable organizations and corporations to help them meet the need.

FORBES: 12 Days of Charitable Giving 2012: Be An Elf

U.S. postal service mail volume, fell to 168 billion pieces in 2011 from the record 213 billion in 2006.

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The mail agency has seen other structural problems in declining mail volume, but has seen growth in it shipping services, up 9% in 2012.

BBC: US Postal Service in $16bn loss