If your homepage has a form and sends out e-mails then it is normally done with php(mail). It is recommended that you use a SMTP server instead.
Go to https://login.admaxhosting.se/knowledgebase/article/14/uppgifter-e-postprogram/ for more information.
As an example with a WordPress site, you can install a plugin that solves it for you. Two examples:
WP Mail SMTP
Easy WP SMTP
Install the SMTP-plugin, authenticate with username (e-mailaddress you have with us) and password. Use port 587 and TLS.