I have been treating them as spam and ignoring the emails, but that just results in follow-ups.
Should I respond to all of them? Any advice?
It is very apparent from the recruiter emails that come in which ones have actually even bothered to read the note. The vast majority haven't which is a good indication they aren't diligent with their clients either. The rest often thank me for having it, or make other statements and are obviously showing signs of competence so I respond back to them.
Since I run my own mailserver I then add the bad recruiters to a block list so email from their domain is rejected at the SMTP level. The reason for blocking the domain not the individual is that recruiters are in the recruitment business - if they can't hire good people for their own business in a field they specialise in, why should they be trusted for IT?
For really vague/template type emails I email the CEO of the company to give them feedback about their recruiters. Generally, they appreciate it.
For competent recruiters, I tell them to have the founder(s), ceo, or whoever is hiring to call me directly at XXX-XXX-XXXX. I like to cut directly to the chase.
That being said you should totally respond to interesting companies, see what they're working on, and then decline politely.
I sometimes respond, but only if I'm in a good mood.