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) and then we run an internal verification process (we check if the MX is configured with a 'catch-all' and if the address is reachable)
If our validation comes back as positive, we add that list to the list of emails found on that domain (which you will find in every export from Soleadify).
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.
Sometimes using an external tool complementary to ours ((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) might increase the accuracy.
If you're interested to learn more about where Soleadify data comes from, please visit this article.