Cannot send messages to remote servers: DNS Lookup failure: Domain mail.example.com does not exist

Symptoms

• Messages cannot be sent to remote mail servers, a bounce message is returned instead:

  MailEnable: Message could not be delivered to some recipients.
  The following recipient(s) could not be reached:
   
   
  Recipient: [SMTP:<...>@example.com]
  Reason: The message could not be delivered because the domain name (example.com) does not appear to be valid.

• The following can be observed in the MailEnable SMTP Debug log (%plesk_dir%Mail ServersMail EnableLoggingSMTPSMTP-Debug-<date>.log):

  MF-E0039: [<...>.MAI] DNS Lookup failure (11001): Domain mail.example.com does not exist.
  ME-E0060: [<...>.MAI] - Message could not be delivered to target domain (example.com). Message returned to Sender.
  MF-E0039: [<...>.MAI] DNS Lookup failure (11002): Could not resolve domain mx.example.com to IP address.

• It is not possible to resolve mail server from the command line:

  C:> nslookup mail.example.com
  Server: UnKnown
  Address: 192.168.0.2

  *** UnKnown can’t find mail.example.com: Unspecified error

Cause

Default DNS resolver does not work correctly, and therefore mail server is unable to send message to remote ones.

Resolution

1. Connect to the server via RDP
2. Change DNS servers in the network adapter configuration to public ones, such as 8.8.4.4 and 8.8.8.8: Google Public DNS: Get Started