I saw a lot of review saying that the email campaign is not sending

I've experienced it too but there's a workaround to make it work.

As a cold emailer, we will often choose the cheap email hosting out there. I just want to let all of you know that in order for you to have a campaign that is sending emails. Your email host should be google.

I can't say about outlook and zoho as I don't have experience with them.

For the warmup, there's no data showing if it's working behind or not but I do receive some random email and I assume that it was the warmup.

Ending thought: It's frustrating to troubleshoot the software that you thought functioning but at the same time I still want to hold into it (even if the refund option is always available) because I don't want to regret later.