According to the System Status Check page in the admin area, my reverse DNS is not set.
It gives me the following error:
Your box's reverse DNS is currently [Not Set], but it should be mydomain.com. Your ISP or cloud provider will have instructions on setting up reverse DNS for your box at 184.108.40.206.
Note that I’ve changed the domain and IP address in the error message.
When I do a manual check using either the host or dig command on my box, the reverse DNS is showing up as being correctly set.
I’m pretty sure this has only started showing up as an error in the status page since the last update but can’t be 100% sure.