Soleadify data is extracted from the business' website. Whenever we find an email address, we check the domain to see if there is an email server for that domain (this is technically called an MX lookup).
If the answer is yes, we add that list to the list of emails found on that domain (which you will find in every export from Soleadify)
We don't verify emails at the moment, although this is on our roadmap for the next 6 months.
There's lots of reasons for why an email listed on a business' website would be invalid - from simple typos, to companies going under without updating their website.
And identifying bad emails before sending is very important - having a clean list when sending outreach campaigns is mandatory for good email deliverability.
Hence, we strongly suggest you use an email validation tool before sending out massive campaigns (I would recommend https://zerobounce.net, but there's little that sets apart one validation tool from the other, so it doesn't really matter which one you use).
If you're interested to learn more about where Soleadify data comes from, please visit this article.