This domain is valid and should be able to receive e-mail.
Using MX pointer mail.mailerhost.net from DNS with priority: 10
You should block this domain for signups/registrations.
This looks like a temporary/disposable e-mail domain.
This domain is specifically blacklisted. There are also multiple heuristics to automatically flag new domains.
Get started using the free API for developers.
Did you know we had a free API to validate e-mails and block ace-mail.net?