Check email MX records and priority of mail exchange servers. Find out if the mail is configured correctly. If the mail does not have the correct SMTP server it can not receive mail.
MX Lookup is tool to verify email address DNS settings. Before the mailbox receives email, the mail server will must find path to this mailbox in the Internet. On this page you can check if the email is located. If the email has the wrong mail server settings, you will examine it and understand how to fix it. DNS server is the first link on the Internet that contains information about email. You need to ensure that the DNS servers work properly and consistently.
Find the mail exchanger for an hostname.
Find mail servers for a domain.
DNS MX Records Lookup.