refactor: use built in smtp library (close #34)

common/email.go

 package common
 
-import "gopkg.in/gomail.v2"
+import (
+	"fmt"
+	"net/smtp"
+	"strings"
+)
 
 func SendEmail(subject string, receiver string, content string) error {
-	m := gomail.NewMessage()
-	m.SetHeader("From", SMTPAccount)
-	m.SetHeader("To", receiver)
-	m.SetHeader("Subject", subject)
-	m.SetBody("text/html", content)
-	d := gomail.NewDialer(SMTPServer, SMTPPort, SMTPAccount, SMTPToken)
-	err := d.DialAndSend(m)
+	mail := []byte(fmt.Sprintf("To: %s\r\n"+
+		"From: %s<%s>\r\n"+
+		"Subject: %s\r\n"+
+		"Content-Type: text/html; charset=UTF-8\r\n\r\n%s\r\n",
+		receiver, SystemName, SMTPAccount, subject, content))
+	auth := smtp.PlainAuth("", SMTPAccount, SMTPToken, SMTPServer)
+	addr := fmt.Sprintf("%s:%d", SMTPServer, SMTPPort)
+	to := strings.Split(receiver, ";")
+	err := smtp.SendMail(addr, auth, SMTPAccount, to, mail)
 	return err
 }

go.mod

@@ -12,8 +12,8 @@ require (
 	github.com/go-playground/validator/v10 v10.12.0
 	github.com/go-redis/redis/v8 v8.11.5
 	github.com/google/uuid v1.3.0
+	github.com/pkoukk/tiktoken-go v0.1.1
 	golang.org/x/crypto v0.8.0
-	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
 	gorm.io/driver/mysql v1.4.3
 	gorm.io/driver/sqlite v1.4.3
 	gorm.io/gorm v1.24.0
@@ -45,7 +45,6 @@ require (
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect
 	github.com/pelletier/go-toml/v2 v2.0.7 // indirect
-	github.com/pkoukk/tiktoken-go v0.1.1 // indirect
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	github.com/ugorji/go/codec v1.2.11 // indirect
 	golang.org/x/arch v0.3.0 // indirect
@@ -53,7 +52,5 @@ require (
 	golang.org/x/sys v0.7.0 // indirect
 	golang.org/x/text v0.9.0 // indirect
 	google.golang.org/protobuf v1.30.0 // indirect
-	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
-	gopkg.in/yaml.v2 v2.4.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )