diff --git a/docs/usage/configuration.md b/docs/usage/configuration.md
index a05c22c..8d246f9 100644
--- a/docs/usage/configuration.md
+++ b/docs/usage/configuration.md
@@ -57,3 +57,5 @@
 - SIGN_SECRET
   - used for signing tokens
   - if not set or set to an empty string, then the features that depend on it are disabled
+- UA_MAIL_BLOCKLIST
+  - List of user agents, separated by comma, that are not allowed to trigger sign in mails
diff --git a/src/api/auth.ts b/src/api/auth.ts
index f70fb17..895f58e 100644
--- a/src/api/auth.ts
+++ b/src/api/auth.ts
@@ -17,7 +17,8 @@
 
 import { json } from 'body-parser'
 import { Router } from 'express'
-import { BadRequest } from 'http-errors'
+import { BadRequest, Forbidden } from 'http-errors'
+import { config } from '../config'
 import { Database } from '../database'
 import { sendLoginCode, signInByMailCode } from '../function/authentication/login-by-mail'
 import { isMailAddressCoveredByWhitelist, isMailServerBlacklisted, sanitizeMailAddress } from '../util/mail'
@@ -49,6 +50,8 @@ export const createAuthRouter = (database: Database) => {
         res.json({ mailAddressNotWhitelisted: true })
       } else if (isMailServerBlacklisted(mail)) {
         res.json({ mailServerBlacklisted: true })
+      } else if (config.uaMailBlocklist.indexOf(req.headers['user-agent'] || '') !== -1) {
+        throw new Forbidden()
       } else {
         const { mailLoginToken } = await sendLoginCode({
           mail,
diff --git a/src/config.ts b/src/config.ts
index 9cd9c40..990d9c7 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -1,6 +1,6 @@
 /*
  * server component for the TimeLimit App
- * Copyright (C) 2019 - 2022 Jonas Lochmann
+ * Copyright (C) 2019 - 2024 Jonas Lochmann
  *
  * This program is free software: you can redistribute it and/or modify
  * it under the terms of the GNU Affero General Public License as
@@ -22,6 +22,7 @@ interface Config {
   pingInterval: number
   alwaysPro: boolean
   signSecret: string
+  uaMailBlocklist: Array<string>
 }
 
 function parseYesNo (value: string) {
@@ -34,12 +35,17 @@ function parseYesNo (value: string) {
   }
 }
 
+function parseList(list: string) {
+  return list.split(',').map((item) => item.trim()).filter((item) => item.length > 0)
+}
+
 class ParseYesNoException extends Error {}
 
 export const config: Config = {
-  mailWhitelist: (process.env.MAIL_WHITELIST || '').split(',').map((item) => item.trim()).filter((item) => item.length > 0),
+  mailWhitelist: parseList(process.env.MAIL_WHITELIST || ''),
   disableSignup: parseYesNo(process.env.DISABLE_SIGNUP || 'no'),
   pingInterval: parseInt(process.env.PING_INTERVAL_SEC || '25', 10) * 1000,
   alwaysPro: process.env.ALWAYS_PRO ? parseYesNo(process.env.ALWAYS_PRO) : false,
-  signSecret: process.env.SIGN_SECRET || ''
+  signSecret: process.env.SIGN_SECRET || '',
+  uaMailBlocklist: parseList(process.env.UA_MAIL_BLOCKLIST || '')
 }