We don't believe in unethical practices (unsolicited emailing would fall under the category of ‘unethical’, by our standards).
The way that we approach an Endorsed Mailing or a Solo Ad, for example, is from the perspective that we are providing a new campaign to a list owner, whose content and typical correspondences with their dedicated subscribers, ideally, aligns with your campaign/niche/mission statement etc. as well. There is power in building relationships, as you will soon begin to see, if you have not realized this, already.
From there, the list owner's subscribers will 'click' on your campaign/link, which the list owner has included in their email correspondence, as a recommendation. You are paying the list owner for a certain number of 'clicks', upfront, or in some cases, you can set this same objection with a list owner who has a similar subscriber count/list size to you, whereas, you may simply ‘swap’, ‘click for click’, rather than running a paid promotion. Oftentimes, the list owner will actually exceed their deliverable for 'number of clicks'--putting emphasis, again, on the power of building relationships.
So, you see, in this scenario, the email subscriber is willingly clicking on your promotion link, and opting into your campaign.