- Plesk for Windows
Unlimited number of mail can be sent despite the fact that Outgoing Mail limits are set for mailbox
SmarterMail Pro edition is set as mail server.
Plesk uses native SmarterMail Throttling feature to handle Outgoing Mail Control.
However, there is SmarterMail Pro edition is installed on the server and such feature is not available for Pro version, only for Enterprise SmarterMail Edition Explanation
To make Throttling feature available consider to upgrade SmarterMail to Enterprise edition.
Or switch to MailEnable mail server.