如果您使用的是本地安装的邮件客户端，您可能已经注意到电子邮件的大小似乎比您附加到的文件大一些。为什么这是一个值得关注的问题？今天的超级用户问答文章对一个困惑的读者的问题有了答案。

今天的问答环节是由SuperUser提供的，SuperUser是Stack Exchange的一个分支，是一个由社区驱动的问答网站分组。

问题

超级用户读者arcèu Lupse想知道为什么他的电子邮件比附件大：

When attaching files to email, I have noticed that Mozilla Thunderbird calculates the total size of the resulting email as much larger than the files I have attached.

Here is a recent example: two images, one at 13 MB and the other at 3.6 MB, approximately 17 MB in total, and there were four lines of text. Mozilla Thunderbird then asked me if I really wanted to send an email with a total size of 22 MB.

Where is that difference in size coming from? Having 5 MB of text sounds like a bit much.

为什么电子邮件的大小会比附件大？

答案

超级用户贡献者DavidSchwartz为我们提供了答案：

Your data was 17 MiB, there are 1024 KiB in a MiB, 1024 B in a KiB, and 8 bits in a byte. So that is a total of 142,606,336 bits.

Base 64 encoding encodes every 6 bits as a separate byte, so we need about 23,767,722 bytes. Dividing by 1024 twice gives us a total of 22.67 MiB. So that is where the 22 MiB comes from.

Email is a pretty old technology and does not assume an 8-bit clean pipe.

有什么要补充的解释吗？在评论中发出声音。想从其他精通技术的Stack Exchange用户那里了解更多答案吗？在这里查看完整的讨论主题。