What should I do?

I'd add a link itno the email summaries, asking for feedback - in return for some free emails or some nice goodies!

If one of the apps I used sent me an email asking for help - but me specifically, not a mass email - I would almost always respond positively.

I'd say go for personal email at this point. You're just starting out and the personal touch will increase odds of getting the feedback.

You can also consider looking at competitors in your market. Specifically, check out reviews of other solutions and see where the frustration points exist.

Start with personal emails. No long text. Short and steady. i've seen the simplest text based emails that I reacted upon, while ignoring fancy-pancy designed ones.

The simple emails show bootstrap mentality, so I'm earlier to recognize actual people instead BigCorp reaching out.

After initial feedback and growing, perhaps start with newsletter that brings value, and reach out after userful content with the question.

Or let it come back in your email footer in the free version or something like that :)

'I want to reach them & collect feedbacks.'

Who is them? Who do you want to reach? Be more specific so we can help more. :)

at the top or bottom of the email, perhaps adding a CTA for a feedback form?

Sending emails personally is great too