mail receive with wrong domain

Hi
I am using contact form7 (version 4.2.2) in my site. When visitor submit the form, they received feedback email like this [ visitor_name via tiga.pelayanweb.com ]. But tiga.pelayanweb.com is not my domain.Please give me suggestion.

https://ww.wp.xz.cn/plugins/contact-form-7/