Return-Path: <user1@example.com>
From: uesr1 <user1@example.com>
To: Yamada Taro <yamada@example.com>,=?UTF-8?B?dXNlcjJAZXhhbXBsZS5jb20=?=
 <user2@example.com>,
 =?UTF-8?B?dXNlcjNAZXhhbXBsZS5jb20=?= <user3@example.com>,
	user4 desu <user4@example.com>
Subject: aaabbbccc123
Content-Type: text/plain

Hello.