Email 定义
一封符合标准的 Email 大致是这个样子的： Mail Header [define boundary "--123"] 2 eol –123 header block 1 [define boundary "--456"] 2eol –456 header block 1.1 2eol content block 1.1 2eol –456 header block 1.2 2eol content block 1.2 2eol –456– 2eol –123 header block 2 2eol content block 2 2eol –123– 2eol