When it comes to sending bulk emails you probably do not want to use your top level domain. Let us take a look at dogwoodlabs.com for example. Most marketers doing a bulk send would really want to use dogwoodlabs.com in a bulk send. Best practice, however, would be to use a sub-domain instead:
The reason for that is to hopefully keep the domain reputation of your top level domain and your bulk sending domain separate. This would help reduce any deliverability impact to your top level domain if something were to go drastically wrong with your bulk sends. Most blacklists do go by the sending ip but there are some that are domain based. If your bulk sending domain gets blacklisted that can have some serious impact to your top level domain where the majority of personal email addresses are set at. Let’s not have that happen to your domain.