feat(mail): 自 go-hua 迁入 SMTP 邮件发送封装

- SendToMail 支持收/抄/密送与回复地址、HTML 或文本正文
- 附测试、examples/mail 例程与包 README(注明不支持 465 加密端口)

mail/mail.go

@@ -0,0 +1,40 @@
+// Package mail 封装 SMTP 邮件发送。
+package mail
+
+import (
+	"net/smtp"
+	"strings"
+)
+
+// SendToMail 通过 SMTP 发送邮件
+// user/password 为 SMTP 账号与密码（或授权码）；host 如 "smtp.example.com:25"
+// mailType 为 "html" 时正文按 HTML 发送，其他值按纯文本发送
+// to/cc/bcc 分别为收件人/抄送/密送列表
+func SendToMail(user, password, host, from, subject, body, mailType, replyToAddress string, to, cc, bcc []string) error {
+	hp := strings.Split(host, ":")
+	auth := smtp.PlainAuth("", user, password, hp[0])
+	var contentType string
+	if mailType == "html" {
+		contentType = "Content-Type: text/" + mailType + "; charset=UTF-8"
+	} else {
+		contentType = "Content-Type: text/plain" + "; charset=UTF-8"
+	}
+
+	ccAddress := strings.Join(cc, ";")
+	bccAddress := strings.Join(bcc, ";")
+	toAddress := strings.Join(to, ";")
+	msg := []byte("To: " + toAddress + "\r\nFrom: " + from + "\r\nSubject: " + subject + "\r\nReply-To: " + replyToAddress + "\r\nCc: " + ccAddress + "\r\nBcc: " + bccAddress + "\r\n" + contentType + "\r\n\r\n" + body)
+
+	sendTo := MergeSlice(to, cc)
+	sendTo = MergeSlice(sendTo, bcc)
+	err := smtp.SendMail(host, auth, user, sendTo, msg)
+	return err
+}
+
+// MergeSlice 合并两个字符串切片（用于合并收件人列表）
+func MergeSlice(s1 []string, s2 []string) []string {
+	slice := make([]string, len(s1)+len(s2))
+	copy(slice, s1)
+	copy(slice[len(s1):], s2)
+	return slice
+}