I am a Moodle/LMS expert with many years of experience. Also, I have my own dozens of customers of Moodle in Australia, so I know Moodle very well.
I can assist you in installing certificate and any other plugins you need, plus I can sort out your email issue. Please note that if your server is sending emails to students, that may be a different issue than Moodle one. Generally, that's SPF, DKIM etc related email issue. No matter what, I will sort out everything.
I am ready to start the work and available on chat.
Thanks
Sij