try ti use the latest version of IPrice calculator LIGHT 1.1.28:
Fixed a bug in the non-sending of an order on some mail servers, when the sender's address did not match the SMTP mailing address. Now the address of the sender of the order letter is taken from the general settings of Joomla (the tab "Server" - "Mail settings", the parameter "From E-mail"). For the correct guaranteed delivery of the order letter, it is recommended in the Joomla preferences to choose the method of sending letters - "SMTP", set the necessary SMTP parameters, and specify the e-mail address of the SMTP account in the "From E-mail" parameter.