By default Piwik will try to detect the current Hostname and use it in all emails sent. In some cases, the hostname cannot be detected and Piwik will use “defaultHostnameIfEmpty.example.org”. You can specify your domain name to appear in From: email addresses by adding the following lines in your config/config.ini.php file:
[mail] defaultHostnameIfEmpty = mydomain.com
This will affect all emails sent from Piwik: Password reminder, Email reports. You can also change the default email address “From:” in PDF reports emails.