Hi Sergey,
Could you check if "siteurl" in table [prefix]_options is with or without "www"? Wordpress will likely try to redirect to its main url so if you force it with Plesk and they are different it will cause a redirect loop.
Hi Hugosnel,
Check this section "Setting Custom Limits for Domains" there http://docs.plesk.com/en-US/12.5/administrator-guide/mail/protection-from-outbound-spam/custom-limits.73368/