I am sure this is the default personal message settings.
So, this is enough to save us from this hassle, but if it's not the default setting, then members should uncheck the tick mark from "Allow newbies to send you PMs" unless you understand the risks. And if you see someone is sending you unsolicited PMs, then simply use the "Report to admin button that will get them banned.
There is an option to receive and don't receive PMs from newbies and depends on your need, you can check or uncheck it. If you are a businessman, with a service in the forum, allowing newbies to send you PMs is almost neccessary for your business. As non-business forum member, if you are experienced, you see no harm in receiving PMs from newbies, except kind of annoyance if any.So, this is enough to save us from this hassle, but if it's not the default setting, then members should uncheck the tick mark from "Allow newbies to send you PMs" unless you understand the risks. And if you see someone is sending you unsolicited PMs, then simply use the "Report to admin button that will get them banned.
This is a personal choice in profile customization, and everyone have different choices.