The location of logs will vary dependant on if the template used had a Parallels Plesk control panel included or not.
With Plesk control panel:
The mail log file is located under /usr/local/psa/var/log/maillog
The location of the http error/access log varies per domain, however, the general syntax is preserved:
Where $Domain_name is replaced with the domain name you want the logs viewed for.
The last set of logs can be viewed from within the Plesk control panel as well. It is available under Website & Domains > Show Advanced Operations > Logs, in the control panel for the domain you are looking to review the logs for.
All the logs are located under /var/log/, brief description of the logs available:
maillog - mail server logs
messages or dmesg (depends on the linux distribution) - holds the main server log
mysql - holds mysql logs
The apache2 directory holds error and access logs for the apache server, named error_log; access_log respecitvely.