Enable Sendmail mail relay in Plesk without authentication

Symptoms: Mails generated by contact forms or scheduled tasks are not sent.

Cause: The Sendmail utility is disabled.

Resolution: Allow users and scripts to use Sendmail.

1. Log in to Plesk.

2. Go to Tools & Settings > Outgoing Mail Control > Subscription > example.com(Select the domain) > Change Limit:

3. Set the Sendmail usage policy to Custom settings for the subscription and enable the option Allow using Sendmail for scripts and users on this subscription.

For more information please follow below mention Plesk KB article:

https://support.plesk.com/hc/en-us/articles/213907645-Mails-generated-by-contact-form[%E2%80%A6]sks-are-not-sent-You-are-not-allowed-to-use-sendmail-utility