您可以使用EncodingUtil类将附件转换为 Base64。
根据MIME标准布置您的电子邮件。
这是一个借来的例子:
Content-Transfer-Encoding: 7bit
Content-Type: multipart/mixed; boundary="_----------=_10167391557129230"
MIME-Version: 1.0
Date: Thu, 21 Mar 2002 19:32:35 UT
From: martin dot zahn at akadia dot ch
To: martin dot zahn at akadia dot ch
Subject: MIME test
X-Mailer: MIME::Lite 2.106 (B2.11; Q2.03)
This is a multi-part message in MIME format.
--_----------=_10167391557129230
Content-Transfer-Encoding: binary
Content-Type: text/plain
Hello world!
--_----------=_10167391557129230
Content-Transfer-Encoding: base64
Content-Type: application/zip; name="test_file.zip"
UEsDBBQAAAAIAEAUmicKJJts5wUAANkOAAAHAAAAaG93LmNnaa1XbW/bRgz+
7AD5D6ziJPJmR8k+DEj8snWd0wRonS51VwxNYcj22bpZ1qm6cx0v8H77SN5J
APsNAAAAAA==
--_----------=_10167391557129230--
.