For outgoing mail, this automatic presentation of the correct certificate doesn't work because Postfix doesn't support it. Instead, we have to sign the Postfix certificate with one certificate that contains every domain on the server that is used for autoconfigured outgoing mail (the LetsEncrypt limit is 100 domains). This means that the main domain in Virtualmin (the parent of the server hostname that we already used to sign the server certificate, let's call it must be configured at Virtualmin > Server Configuration > Website Options with "Default website for IP address?" set to "Yes" and for all other domains the setting "Website matches all sub-domains?" must be set to "No".
TMDHosting services has been around since 2007 providing users with a diverse set of hosting options. They offer fast VPS solutions that include generous amounts of disk space and bandwidth with the physical servers being located in either the US, Singapore or the Netherlands. Their VPS prices are in line with what you would expect for the level of service you are getting, which includes powerful CPUs and plenty of RAM.
It comes down to basic reasons: If your business is growing and receiving more traffic, it is time to move to a more controlled setting like VPS.

Partitioning a single server to appear as multiple servers has been increasingly common on microcomputers since the launch of VMware ESX Server in 2001. The physical server typically runs a hypervisor which is tasked with creating, releasing, and managing the resources of "guest" operating systems, or virtual machines. These guest operating systems are allocated a share of resources of the physical server, typically in a manner in which the guest is not aware of any other physical resources save for those allocated to it by the hypervisor. As a VPS runs its own copy of its operating system, customers have superuser-level access to that operating system instance, and can install almost any software that runs on the OS; however, due to the number of virtualization clients typically running on a single machine, a VPS generally has limited processor time, RAM, and disk space.[2]

The most obvious and popular reason for a VPS is to run a single website, or multiple websites. However, you can use them for pretty much anything that requires access to the internet – such as a web application like Nextcloud to run your own Dropbox alternative – or to create your own virtual private network to better secure the internet connection of your PCs and mobile devices.