None of the Users are receiving mail from external domains
- Users are able to receive mail from other users on the local domain
- None of the Users are able to receive mail from external domains
- The mail queue on the mail server is empty
- The MX pointer for the email domain has got changed and so external senders are not connecting to the active setup.
- The server has got disconnected from the Internet and so external senders are unable to connect to the active servers.
- The email domain has expired and therefore all its DNS records are wiped out. As a result the mail servers pertaining to this email domain cannot be found on the Internet.
- The external mail are landing on the gateway server or service (possibly a third party security appliance or mail cleaning service) and are held in the queue there.
- The public IP of the server (natting in the firewall) has got changed and hence external senders are unable to find the server.
- If the MX landing server for the email domain is a Mithi server, possibly the AUTHREQUIRED attribute has been Enabled for the "default" smtp control. This will require that the senders must authenticate even before they can deliver to a local user (which is not possible)
- DNS Records: Using the following command, confirm that the DNS records are active and proper. The IP address or host name got from the below command should be the same as this mail/relay server
host -t MX <email domain name> If this provides a valid output (points to this mail/relay server), we can assume that the DNS records are active and the MX records are valid and proper. If this is not proper (not giving any output or not pointing to the servers in the active setup, contact the network service provider for help to rectify this.
- Network: From an external server or PC, check that you can ping to and telnet to the MX landing point for this domain.
ping <MX server IP/host name got from the above command> telnet <MX server IP/host name got from the above command> 25 If this works fine, then we can assume that the MX landing point is accessible from outside over the published public IP or host name. If this doesn't work out, then you may need to check with the cleaning mail service provider OR the network connections and NAT settings in the firewall which lead to the MX landing server/appliance. You may contact your network service provider for support on this.
- Test sending a mail: Send a test mail using telnet <MX server IP/host name got from the above command> 25 from an external server or PC. If this test is able to deliver the mail to the MX landing server, then it means that the external mail are being accepted by the MX landing server.
If this test fails, you may need to contact your clean mail service provider OR the provider of the security appliance/Relay server to further investigate. If this test succeeds but you receive a bounce stating that you would need to authenticate before you can send this mail, you may need to verify that the AUTHREQUIRED attribute on the MX landing server (If it is Mithi's Connect XF configured as a relay server) is OFF.
- Connection from the Relay server/security appliance/clean mail service to the Mail server
Check on the Relay server or security appliance or clean mail service as to whether they are holding the mail in the queue. If that is so, what is the reason and to resolve that.