Sending email fails with connection timeout: [smtp-host]:25 ... Caused by: Couldn't connect to host, port: [smtp-host], 25

Issue

Due to port 25 being blocked on 3 August 2026, applications hosted in Mendix Cloud that send emails over that port experience connection timeouts when trying to reach the SMTP server on port 25. Errors resemble the following:

org.apache.commons.mail.EmailException: Sending the email to the following server failed: [smtp-host]:25 ... Caused by: Couldn't connect to host, port: [smtp-host], 25; timeout 60000 ... Caused by: connect timed out

Environment

Applications hosted in Mendix Cloud

Cause

Sending email from Mendix Cloud over port 25 is not supported, as mentioned in the Sending Email documentation. Using port 25 may block email sending for all customers in the same cluster and violates policy, so this configuration cannot be changed by the customer. In this case, port 25 was blocked for all Mendix Cloud clusters (excluding Dedicated Cloud), causing outbound SMTP connections over port 25 to time out and email delivery to fail.

Solution/Workaround

Because port 25 cannot be used to send email from Mendix Cloud, the SMTP configuration must be changed to use a secure port. To resolve the issue:

1. Confirm that your SMTP provider exposes a secure port such as 587, which is a best practice offered by most modern providers.
2. Change the SMTP configuration in the application from port 25 to a secure port such as 587.
3. Test the change in a lower environment (for example, UAT) to confirm that email delivery succeeds.
4. Once validated, apply the change to the Production environment.

Additional information

Mendix documentation: Sending Email