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What is the difference between the different CDOSYS modules or methods?
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In versions of Windows Server previous to Windows 2003 Server, for sending outgoing email from within ASP applications, Microsoft provided a software component called CDONTS that was very well suited for this purpose. The CDONTS component interfaced with the Microsoft SMTP Service which was able to efficiently deliver outgoing email. Since the CDONTS component actually queued up outgoing email and allowed the Microsoft SMTP Service to deliver them separately from the controlling application which was generating them, it was an excellent solution for performance oriented installations. However CDONTS had to be properly configured on the server side, before it could be used for sending any outbound email.
When Microsoft released Windows 2000 Server, they introduced a completely new method for working with the Microsoft SMTP Service. They replaced CDONTS with a new component interface called CDOSYS. CDOSYS is able to support all the functionality that was found in CDONTS and more. Actually, CDOSYS provides significantly more functionality than just the ability to send outbound email, but for the purpose of our ASP web server applications, that is really the only focus here. Whereas the older CDONTS only provided one method for sending outbound email, the CDOSYS component provides multiple methods. For our purposes, we support two different “flavors” to CDOSYS.
The first type we refer to as CDOSYS Pickup. The CDOSYS Pickup method of sending outgoing email is nearly identical to the original way that the CDONTS component worked. The component will queue up outgoing email for delivery by the Microsoft SMTP Service. Like CDONTS, the CDOSYS Pickup method requires that the Microsoft SMTP Service is configured on the server side to deliver outgoing email. This is done by your web host or ISP and doesn’t require any configuration on your part. If you are using your own server, you must be able to properly configure the Microsoft SMTP Service to deliver or forward outbound email through a valid SMTP server for your network. The benefits to the CDOSYS Pickup method is the same as the original CDONTS, in that this technique queues outbound email and allows the web server application to be much more responsive to your end users. This is the preferred method for using CDOSYS.
The second type we refer to as CDOSYS Port. This CDOSYS Port method of sending outgoing email works nearly the same as most other third-party Email COM components that can be used for sending SMTP email. It allows the application to send the email message directly to a forwarding mail server for delivery. Like these other components, it does this in real-time by communicating directly with the forwarding SMTP server. Since each email message being sent must wait for proper response from the forwarding SMTP server, this can slow application performance on busy servers or when using a slower or heavily loaded email server. This method of using CDOSYS works very well and for our purposes is identical to almost all other supported email components.
Additional Info: While CDOSYS was introduced with Windows 2000 Server, CDONTS was also still included. However CDONTS is no longer included on newer versions of Windows Server starting with Windows 2003 Server. Versions of Windows 2003 Server and later will only support CDOSYS.
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