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SMTP Relay Blocking Error Message When You Send Messages
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This article was previously published under Q290842
SYMPTOMS
When you send messages you, may receive an error message
that your message cannot be sent because of Simple Mail
Transfer Protocol (SMTP) relay blocking. The exact error
message may vary, depending on your Internet service
provider (ISP). However, it is similar to the following
error message:
The message could not be sent because one of the
recipients was rejected by the server. The rejected e-
mail address was '<
[email protected]>'.
Subject: '<Test>', Account: '<Test>',
Server: '<smtp.example.com>', Protocol: SMTP, Server
Response: '550 <
[email protected]>... Relaying Denied',
Port: 25, Secure (SSL): No, Server Error: 550, Error
Number: 0x800CCC79
CAUSE
This behavior may occur if you have one of the following
configurations:
You are logged on to a Local Area Network (LAN) that has
an Internet gateway and you try to send messages through
an ISP's SMTP gateway.
You are logged on to an ISP and you try to send messages
through another ISP's SMTP gateway.
You are using a cable modem or ADSL to get to another ISP
and you try to send messages.
This behavior affects all messaging clients, regardless
of the manufacturer.
RESOLUTION
To resolve this behavior, contact your ISP for help. The
e-mail client does not cause this behavior. From a
messaging client standpoint, there are no solutions for
customers whose ISPs block all SMTP Relay traffic.
Most of the new SMTP e-mail gateway software permits
relaying for specific IP addresses. This is how cable
modem and ADSL users can continue to use their same ISP.
The cable modem or ADSL provider must provide the
customer a static IP address, in turn, the customer's e-
mail ISP allows relaying for that specific IP address.
Banks of IP addresses can also be permitted, which may
provide a work around for some corporate customers who
access ISPs through their corporate LAN.
If the error message that is described in the "Symptoms"
section of this article is random, it is possible that
your SMTP server is checking whether the domain or the
recipient name actually exists before sending the
message. If the recipient's e-mail server is temporarily
down or unavailable for another reason, such as high
network volume, your SMTP server cannot verify the
address and may reject the relay. In this case, action is
not required. The message is sent when the receiving
server is available again.
MORE INFORMATION
This behavior may become more common as ISPs start to
take action against SPAM messages. SPAM is flooding the
Internet with many copies of the same message in an
attempt to send the message to people who would not
otherwise choose to receive it. Most SPAM messages use an
automated system to send commercial advertising, or mass
marketing messages. SPAM costs the sender very little to
send; most of the costs are paid for by the recipient or
the e-mail providers.
Some ISP's are fighting SPAM by requiring each user to be
dialed directly into their system to send messages
through their SMTP gateway. This is an easy way to
control SPAM, but may affect some users who tunnel into
their e-mail account from another ISP.
MSN, the Microsoft Network, is one example of an ISP that
has imposed SPAM blocking. Additionally, MSN has imposed
restrictions whereby if the e-mail address in your
Internet Account properties does not match that of your
MSN account, you may also receive SMTP blocking errors.
This affects users who receive messages with two
different Internet addresses, but that want the same
reply address on both e-mail accounts. Other ISP's
implement similar strategies.
To send or receive messages through a LAN, additional ISP
or DSL and similar connection devices through MSN, the
SMTP server settings must be set to secure.
MSN e-mail server settings for a LAN, DSL or third-party
connection must be set to secure.smtp.email.msn.com.
Examples of SMTP Relay Blocking
Employees have personal ISP accounts at isp.com where
isp.com is your Service Provider's domain name. They use
the company's corporate LAN to access their isp.com
messages, and they have any problems sending or
receiving. One day they start receiving SMTP blocking
errors when they try to reply to messages that they have
received from isp.com. They contact isp.com technical
support and are told that isp.com just installed new SMTP
gateway software which prevents SMTP relaying. Now the
employees can receive messages through the LAN, but
cannot send messages because they're not connected
directly to isp.com.
A user has two ISP accounts, one with isp.com and one
with myisp.net, where isp.com and myisp.net are the
Service Providers' domain names. The user dials into
myisp.net and can send and receive messages from both
accounts without problems. One day the user connects to
myisp.net and tries to send messages through isp.com and
receives blocking errors. The user connects directly to
isp.com and can still send and receive messages with both
accounts. In this example, isp.com implemented SMTP relay
blocking and myisp.net did not.
The information in this article applies to:
Microsoft Office Outlook 2003
Microsoft Outlook 2002
Last Reviewed: 9/19/2003 (1.3)
Keywords: kberrmsg kbprb KB290842
