Everybody thinks that the only thing you need to watch out for on email is to get out of the spam box. But, there are actually several steps to having an email gets delivered to the person that you are trying to reach before that system even decides to put it in the spam box or not. That process is called deliverability. Deliverability has a number of factors in it. Some of them can be related to your domain or whether you're on a blacklist, do you have the correct thing set up in your DNS settings for that. Those are all technical requirements.