Following is a list of items that can internet email sent by Microsoft Exchange Server to not be received:
- Your Internet Service Provider (ISP) has blocked all access to the internet because they have received numerous complaints regarding Unsolicited Bulk Email (UBE) and/or other unacceptable traffic originating from a computer or computers on your network. To resolve this issue, contact your Internet Service Provider and request that the block be removed.
- Your Internet Service Provider (ISP) has appled an SMTP Filter also called a Port 25 Block to your Internet Service at any time without notification or consent. In doing so, all outbound email sent from Microsoft Exchange Server will no longer route. After a period of time, you will very likely receive multiple Non-Delivery Reports (NDR) in Microsoft Windows Server Event Viewer and within Microsoft Outlook. To resolve this issue, contact your Internet Service Provider and request that the block be removed.
- Your Internet Service Provider (ISP) has moved or taken offline their Domain Name Servers (DNS). The Domain Name Servers can be defined in the TCP/IP Configuration on the Windows Server that houses Microsoft Exchange Server as well as within Windows Server - DNS Server to forward DNS Requests. The latter being the proper configuration. To resolve this issue, contact your Internet Service Provider and request the TCP/IP Addresses of the new Domain Name Servers or a timeline of when the existing Domain Name Servers will be back online.
- A change has been made to an internal Firewall which is now blocking SMTP Port 25.
- A change has been made to the Internet Router/Gateway which now prevents the Windows Server that houses Microsoft Exchange Server from accessing the Internet.
- The Exchange Information Store has been dismounted by Microsoft Exchange Server. In this scenario, both internal and external email would no longer route. Microsoft Outlook would be forced offline.
- The Simple Mail Transfer Protocol (SMTP) Service has Stopped.
- The DNS Server Service has Stopped.
- An unusually large email is being sent or received by Microsoft Exchange Server.
- Microsoft Exchange Server has been improperly configured and is being exploited using an Open Relay.
- Microsoft Exchange Server has been corrupted by a virus infection.
- The Forward and/or Reverse DNS Entry for your Mail Server has been removed from the Root Servers.
- The receiving Mail Server may have a Grey List or Black List in place that is preventing the email from being received.
- Your Mail Server has been added to a Real Time Blackhole List (RBL). Determine the Hostname/IP Address of your Mail Server and then enter its IP Address into the RBL Lookup.
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