Troubleshoot SMTP Configuration Issues


This article explains how to troubleshoot issues that may arise during Simple Mail Transfer Protocol (SMTP) configuration. In case you have followed the set-up steps in this article, and have checked for specific setup requirements from Google Apps or Microsoft Office 365, but are presented with an error message, you can find a list of possible issues and potential solutions in the table below.

We recommend involving your IT department when troubleshooting SMTP configuration issues.

Issue Potential Solution

Your company e-mail address is a shared mailbox

A shared mailbox can be accessed by several users, who can send e-mails from it. However, a shared mailbox doesn't have its own username and password. As a result, users can't log into it directly. The login happens via the user's personal mailbox. With regard to Personio, this means that two essential components of the SMTP settings - the username and the password - are not provided.

Use a fully licensed recruiting e-mail address rather than a shared mailbox.

For more information, see the article Setting Up an SMTP Link Between Personio and Frequently Used E-mail Providers.

A firewall allows only certain IPs to be sent via your SMTP server

Your SMTP server only allows e-mails to be sent from certain documented IP addresses.

To ensure that the process runs smoothly, whitelist the following Personio Recruiting IP addresses: 


Connection to external apps cannot be established

You are already using a fully licensed recruiting e-mail address, and you have whitelisted the relevant Personio Recruiting IP addresses, but the connection to external apps cannot be established.

Check if your e-mail account is permitted to connect to external apps. For example, the default setting in Gmail is that it is not allowed.

Enable the use of external apps in your e-mail provider settings.

For more information on troubleshooting steps for Gmail, see the Gmail Help article Check Gmail Through Other Email Platforms.

For more information on managing access to less secure apps, see the Google Workspace Admin Help article Control Access to Less Secure Apps.


A 'wrong credentials' error message is displayed In addition to updating the credentials on your e-mail server, you also need to check that the credentials have been updated within the Personio application by navigating to Settings > Recruiting > General > Recruiting email settings
A 'timeout' error message is displayed Contact your IT department and check if the e-mail server can be reached.

Microsoft 365 authentication issues

The following error message is displayed:

Failed to authenticate on SMTP server with username "" using 2 possible authenticators. Authenticator LOGIN returned Expected response code 235 but got code "535"

This is a common error. You need to ensure that SMTP AUTH is enabled. 

For more information about enabling SMTP AUTH, see the Microsoft Help article Enable or Disable Authenticated Client SMTP Submission (SMTP AUTH) in Exchange Online.

For more information about troubleshooting Microsoft 365 authentication issues, see the Microsoft 365 Help article How to Set Up a Multifunction Device or Application to Send Email using Microsoft 365 or Office 365



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