Probably a better question to ask is . . .

How effective is it in generating engagement with your prospect?

Legalities are often a matter of interpretation and application of the law and most people here don't have the expertise to give you a blanket answer; especially not knowing what your blog commenting requirements and policies are.

I can tell you without question that having a few engaged subscribers that want to hear from you is worth much much more than dozens and dozens of cold non-engaged prospects.

It's best, IMO, to have a simple, well-explained policy in plain sight at your blog explaining how you use the commentor's email address.

The very best to you,

Steve

It's not about legal or not but rather about how you explained to visitors
your mailing campaign policies and if they consented to receive your mail.

If not, you are spammer and there is good chance your hosting company
or free-for-all providers will ban you if you continue to send your newsletters.



fastreplies

It is not permission based, hence no! If you really want to do it, you can casually ask them via email, hey i noticed u commented on the blog and i really appreciate that. Would u mind if i put you in my newsletter for future posts? I promise to never share your email and also you can unsubscribe whenever you want to. If they say , "yes u can put me in your email list , you will be in much better place."

You don't have an opt-in form for your newsletter on your blog pages? Really?

If they like what they're reading, there's a chance they might subscribe. If not - well, there ya' go.

No.

This is spam.

Post an opt-in form on your blog. Give readers the option to join your list.

The best and most ethic way to do this is to create an opt-in form that will be somewhere on your page & also used as a pop-up.

In this way they will give you permission to send them emails whilst making your job easier and also allowing you to send them automated follow-up emails for creating goodwill with your audience and also making offers to them aka pitching your product/affiliate product.

You could probably send one personal email as a reply but certainly don't add them to any mailing lists. They need to know what they are signing up for and they haven't agreed to receive your newsletter yet.


You could send a manual 'thank you' email and invite them to join your list. That should be OK.

I suggest an opt-in form to join your mailing list rather than sending them emails without consent because that's totally spam.

Or if you really want to send them emails, try to make it personal by letting them know that you have seen their comment & ask them whether they would like to receive more emails, etc.

It's for your own site's good