Self-clean-up Email list is insufficient. I would suggest you to get a third party to verify your list before send. I found several email list clean up company where we have no relation with them and not sure the service level. You can try to contact them.
https://www.zerobounce.net/
https://myemailverifier.com/pricing
https://www.millionverifier.com/
https://quickemailverification.com/
https://www.emaillistverify.com/pricing
https://www.mailboxvalidator.com/
https://www.emailmarker.com/
https://www.towerdata.com/pricing
https://www.datavalidation.com/
https://www.xverify.com/
