fix: proper smtp relay, therefore required new config parameter

cmd/bs1in/config.go

@@ -21,6 +21,7 @@ type Config struct {
 	MariaDbPort        string `json:"mariadb_port"`
 	MailUser           string `json:"mail_user"`
 	MailPass           string `json:"mail_pass"`
+	MailSmtpUser       string `json:"mail_smtp_user"`
 	MailSmtpServer     string `json:"mail_smtp_server"`
 	MailSmtpPort       string `json:"mail_smtp_port"`
 	UserCreationSecret string `json:"user_creation_secret"`

cmd/bs1in/mail.go

@@ -16,7 +16,7 @@ Content-Type: text/plain; charset="UTF-8"
 `
 	header = fmt.Sprintf(header, from, to, subject)
 	mailTxt = header + mailTxt
-	auth := smtp.PlainAuth("", from, config.MailPass, config.MailSmtpServer)
+	auth := smtp.PlainAuth("", config.MailSmtpUser, config.MailPass, config.MailSmtpServer)
 	err := smtp.SendMail(config.MailSmtpServer+":"+config.MailSmtpPort, auth, from, []string{to}, []byte(mailTxt))
 	return err
 }