Hello @tngcrdit2021,
If that is the problem then you only need to recreate the symlink.
Option 1 (use parameter f to overwrite the existing symlink):
ln -sf /etc/letsencrypt/live/mail.firstchoiceinvst.com/privkey.pem /etc/ssl/private/iRedMail.key
Option 2 (remove the wrong symlink and create a new one):
rm /etc/ssl/private/iRedMail.key
ln -s /etc/letsencrypt/live/mail.firstchoiceinvst.com/privkey.pem /etc/ssl/private/iRedMail.key
Also, in this command:
root@mail:~# ln -s /etc/letsencrypt/live/mail.firstchoiceinvst.com/ fullchain.pem /etc/ssl/certs/iRedMail.crt
There is an space between / and fullchain.pem, don't know if that is because a wrong copy/paste or because you really used that command.
You should double check that created symlinks are the right ones.
Cheers,
sahsanu