ENT2001: Attempt to Send an E-mail Message Generates Error 5550 (299916)

SYMPTOMS

When you attempt to send an e-mail message, you may receive an error message that cites Error 5550 and states that your e-mail cannot be sent because of Simple Mail Transport Protocol (SMTP) relay blocking.

CAUSE

This error can be the result of any of the following e-mail configurations:

You are logged on to a local area network (LAN) that has an Internet gateway, and you attempt to send e-mail through the Internet Service Provider (ISP) SMTP gateway.
You are logged on to an ISP, and you attempt to send e-mail through another ISP's SMTP gateway.
You are using a cable modem or an Asymmetric Digital Subscriber Line (ADSL) to get to another ISP, and you attempt to send e-mail through that ISP's SMTP gateway. Note that this issue affects all messaging clients, regardless of the manufacturer.

MORE INFORMATION

Because this issue is not caused by the e-mail client, you must contact your ISP for information about how to resolve the issue. There is currently no known resolution of the issue if an ISP blocks all SMTP relay traffic.

Most of the new software for SMTP e-mail gateways allows relay for specific IP addresses. Cable modem or ADSL providers must provide a static IP address for the customer; the customer's e-mail ISP allows relaying for that specific IP address. Banks of IP addresses can also be allowed, which can provide a workaround for some corporate customers who access ISPs through the corporate LAN.

If the error occurs randomly, your SMTP server may be checking to verify that the domain or the recipient name actually exists before sending the message. If the recipient's mail server is temporarily unavailable for some reason, such as high network volume, your SMTP server cannot verify the address and may reject the relay. In this case, no action is required. The message is sent when the receiving server is again available.