I just looked through my Spam folder. I have 48 messages in the month to date. 18 of them are from at least ten domain names matching /^(marketexec|marketexecmail|market-exec)?\d{1,2}\.co\.uk$/. Domains cost money, but not that much, and people do do things like this.
(There’s also the problem of senders aggregating messages from untrusted parties, so that reputation is always a tricky balance. For example, I have four spam messages from gmail.com this month. When I’m not getting bursts like this marketexecmail stuff that started two weeks ago and will probably stop within another couple of weeks, I find that at least a quarter of my spam messages come from gmail.com, outlook.com or hotmail.com; in January, it’s 12⁄46, and at least four more are from other general-public domain names that I recognise.)
(There’s also the problem of senders aggregating messages from untrusted parties, so that reputation is always a tricky balance. For example, I have four spam messages from gmail.com this month. When I’m not getting bursts like this marketexecmail stuff that started two weeks ago and will probably stop within another couple of weeks, I find that at least a quarter of my spam messages come from gmail.com, outlook.com or hotmail.com; in January, it’s 12⁄46, and at least four more are from other general-public domain names that I recognise.)