Topic

After trying to configure your Nintex Automation (K2) environment to use Gmail SMTP to send emails, you face the following error when running your workflow:

There is no connection string for the destination email address ...@gmail.com

If you check the HostServer logs, the following error is logged:

Verify the SMTP connection strings are correct and that SMTP is working properly. Exception: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.7.0 Authentication Required.

The error in HostServer logs suggest the Gmail SMTP server is not allowing the connection as the authentication is wrong.

Instructions 

If you want to use Gmail's SMTP server, you need to make sure the SMTP connection string is setup correctly. You can use ConnectionStringEditor.exe located in iProgram Files]\K2\Host Server\Bin on your K2 server to do that.

Here are the settings you should use for the SMTP connection string:

Authentication: Plain
Server: smtp.gmail.com
Port: 587
TLS: StartTLS
User ID: <your Gmail username>
Password: <see below>

For the password, you can try using your Gmail password, but if you have configured 2FA on your Gmail account, you will need to generate an app password on Google.

1. Logon to https://myaccount.google.com/security
2. Scroll down to see if 2-Step Verification is enabled
3. If 2-Step Verification is enabled, go to https://myaccount.google.com/apppasswords
4. Enter a suitable app name, click Create
5. An app password will be generated. Copy and save the app password somewhere. Make sure this app password is kept safe and not shared as this app password can grant access to your Google account.
6. Go to your K2 server, open ConnectionStringEditor.exe, edit your existing SMTP connection string, and replace the password with the app password generated in step 5
7. Save the changes
8. Restart "K2 Server" service for the changes to take effect

Please note the steps provided are based off the security measures implemented by Google at the time of writing this article. If Google introduced new security measures or policies for their Gmail SMTP servers, these steps may not work.