As a software engineer with a non-zero internet presence, I get emails like this all the time:
Hi [CANDIDATE NAME HERE],
I am [RECRUITER NAME HERE] and I work with [TECH COMPANY HERE].
I came across your [INTERNET SITE HERE] profile and wanted to reach out (always with the "reaching out") to blah blah. Our team is the [SUPERLATIVE HERE] and we work on fast paced problems, and I think you would be a great fit for [TEAM NAME HERE].
If you're interested, let's connect!
Call me maybe?
[RECRUITER NAME HERE]
[CORPORATE EMAIL SIGNATURE HERE]
I've never replied to one of these - not once. After a week or two, they'll send me a reminder, then maybe a third, then they'll disappear for a few months. Eventually I just archive the emails.
It's not that I'm completely opposed to the idea, I just really don't know what to say. The only time I've gone through with one of these was when the person actually found my phone number and I had to say something to them. I've gotten all of my other jobs through application or through people I know closely. Do I just reply with my resume? What else do I say? They want to talk on the phone usually, am I supposed to suggest the times, or will they do that?
They're approaching me, so it's not like I'm particularly crazy about [TECH COMPANY HERE] (I save aggressively and don't really need a job, although I do have one that pays very well), but I could be open to it.
In general I am most interested in replying to first-party recruiters, third-party recruiters really sketch me out.