diff --git a/src/api/auth.ts b/src/api/auth.ts
index 11a746b..7c2cc9f 100644
--- a/src/api/auth.ts
+++ b/src/api/auth.ts
@@ -20,11 +20,11 @@ import { Router } from 'express'
 import { BadRequest } from 'http-errors'
 import { Database } from '../database'
 import { sendLoginCode, signInByMailCode } from '../function/authentication/login-by-mail'
+import { isMailServerBlacklisted } from '../util/mail'
 import {
   isSendMailLoginCodeRequest,
   isSignInByMailCodeRequest
 } from './validator'
-import { isMailServerBlacklisted } from '../util/mail'
 
 export const createAuthRouter = (database: Database) => {
   const router = Router()
diff --git a/src/util/mail.ts b/src/util/mail.ts
index 71d8790..7421d7b 100644
--- a/src/util/mail.ts
+++ b/src/util/mail.ts
@@ -83,7 +83,7 @@ export const sendUninstallWarningMail = async ({ receiver, deviceName }: {
   })
 }
 
-export function isMailServerBlacklisted(mail: string) {
+export function isMailServerBlacklisted (mail: string) {
   const parts = mail.split('@')
   const domain = parts[parts.length - 1]