Email only possible via exim

Hello, I have the following problem, I run an online shop, and I blackmailed that I should pay. I already have a heavily hired CSF firewall doing good work. I have through the ddos attak also clouldflare in use my ip address hidden, now for a fee. I can protect my ip address via cloudflare, but the problem is that I send emails via shop, and there is only the attitude PHP function mail () use (recommended, works in most cases) this works but if I submit my data from the email below Use my own SMTP settings (ONLY for experts) then I always get an error and can not send mails, this error is annoying me Error: Please check your settings Connection could not be established with host mail.runbox.com [# 0] I've already tried some mail try it in with no. the problem is if i use this will release the server domain / ip in the mail PHP function mail () use (recommended, works in most cases) this works I want to protect this, where is my fault ..? I practically want to send the mails externally