Login to the Plesk control panel
Once logged in, click on Mail tab on the top.
On the Mail page click on the email address tab and click on the email address for which you want to create an email alias.
On the next page click on Email Aliases tab.
In Email Alias box, provide the desired email ID which you’d like to be used as an email alias. Make sure its an existing email address.
Click On OK button and you are done