The bulk email checker is very conservative with what it suggests are “correct” emails.
It should do a decent job of identifying correct emails at large companies (i.e. they have a IT department).
But it can fail for smaller businesses.
For example your email/domain failed for a DMARC record, SPF and you’re on two blacklists. So your email is coming up as a error in the tool.
This was a useful exercise as you should set up DMARC and SPF for your email domain ASAP. That will help with deliverability in a big way.
I think you’re using Google mail –
DMARC – https://apps.google.com/supportwidget/articlehome?hl=en&article_url=https%3A%2F%2Fsupport.google.com%2Fa%2Fanswer%2F2466563%3Fhl%3Den&product_context=2466563&product_name=UnuFlow&trigger_context=a
SFP – https://apps.google.com/supportwidget/articlehome?hl=en&article_url=https%3A%2F%2Fsupport.google.com%2Fa%2Fanswer%2F10685031%3Fhl%3Den&product_context=10685031&product_name=UnuFlow&trigger_context=a
But when cleaning your email list you’ll have to use your gut as to if an email has failed becaues it’s wrong or because it’s not been set up correctly by the organisation.