- Windows Server
- Internet Information Services
When attempting to send an email using CDO under Windows Server you receive the following unspecific error message from your application debugger or web browser session:
Your application is unable to relay email into the SMTP system.
The CDO error message is certainly due to your configuration of the SMTP server, or CDO’s inability to raise the stated SMTP server.
A frequent cause of this error message comes from messages with lengthy message lines. It is common place within SMTP systems to refuse to transmit text lines that are greater than around 1000 characters (including the CRLF).
This does not mean that the message itself cannot be greater than 1000 characters, but that individual lines before the carriage return must be less than or equal to 998 characters (the CR [carriage return] and the LF [line feed] count as the remaining two characters).
This rule applies to plain text and to HTML messages. Ensure that your messages comply with this rule.
Ensure that your ISP does not require authenticated SMTP access. If they do, you will need to modify your CDO connector to include authentication. In ASP this is achieved through the addition of the following lines into the CDO settings.
.Item(cdoSMTPAuthenticate) = cdoBasic
.Item(cdoSendUserName) = “YOUR-USER-NAME”
.Item(cdoSendPassword) = “YOUR-PASSWORD”
Ensure that your system is able to connect to to the SMTP service port. A quick trick to check for SMTP connectivity without relying upon port scanners is:
- Open a command prompt
telnet <fully-qualified-domain-name / SMTP Server IP address> 25For example: telnet smtp.www.c-amie.co.uk 25
- If the path to your SMTP server is being blocked you will see the following message
Connecting To <server>…Could not open connection to the host, on port 25 : Connect failed
If your server is unable to access the STMP network, then this error message is consistent with such a failure. The most likely cause of such a block is a firewall rule from a software firewall or a rule configured on a hardware firewall by the network administrator.
An additional consideration to make while checking for connectivity is the impact that Anti-Virus and real-time Anti-Spyware products may have. For example, McAfee Virus Scan Enterprise 8.0.0i makes use of an anti-spyware rule that prevents mass mailing worms from sending email. McAfee will block the SMTP port by default and must be configured to allow IIS (or your application) to relay email.
To reconfigure McAfee Enterprise 8.0.0i:
- Open Virus Scan Console
- Double click Access Protection
- Highlight the “Prevent mass mailing worms from sending email” and click Edit
- For IIS 6.0 running in with standard IIS 6.0 application protection add w3wp.exe to the exceptions list.
For application you will need to query the McAfee log file for the executable name involved in the error message. By default this log can be found at:
C:\Documents and Settings\All Users\Application Data\Network Associates\VirusScan\AccessProtectionLog.txt