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New in version 3.0
Click here for a list of new features in 3.0

Do you have a mailing list? Do you collect email addresses? Are you tired of getting bounce backs every time you perform a mailing? aspNetMX will solve your email validation problems.

aspNetMX is an assembly that requires the Microsoft .NET framework to run. It is used to validate email addresses at different levels. aspNetMX does not have a GUI front end, it is a server component that can only be accessed programmatically.

aspNetMX can be used on signup forms or it can validate huge lists of email addresses from one address to millions. It has built in high performance features that aren't found anywhere else. After almost a year in development and planning, aspNetMX will solve all of your email validation problems.

aspNetMX validates email addresses at four different levels. Syntax, MXRecords (Domain), SMTP, and Mailbox levels. To validate an email address, simply create the aspNetMX object, pass it the email address and the level of validation to check, and aspNetMX will do the rest. For some code examples on how to use aspNetMX, click here.

aspNetMX does not actually send an email, but it can check the remote mail server to see if the server will accept an email for that address. The only way to truly check to see if an email address is valid, is to send an email. Here's a more detailed explanation of the 4 levels of validation provided by aspNetMX.

The syntax level is the easiest validation to perform. When an email is checked for MXValidateLevel.Syntax, the email address is verified to be syntactically correct.

aspNetMX checks to see if an email address is both syntactically correct and makes a DNS network call to verify the domain name part of an email address has MX Records.

aspNetMX checks all of the above levels, and opens a network connection to the remote email address's mail server, to verify the mail server does exist. aspNetMX then immedately closes the connection.

aspNetMX checks all of the above levels, however, if the server is greylisting SMTP commands, the GreyListed level will be returned.

aspNetMX checks all of the above levels, plus, aspNetMX initiates standard RFC SMTP commands against the remote mail server to validate the mail server will accept an email for the address.

When Validate() is executed, it attempts to validate an email address UP TO the level that was specified. If the validation was successful, it returns that level. If the validation was NOT successful, it returns the last highest level of validation that was found. This allows you to vary actions, based upon the level of validation returned. For example

Allows you to take different actions based upon the result from aspNetMX. If only MXValidateLevel.MXRecords was achieved, perhaps a network connection was down, and the email address could be flagged for later validation, where as if MXValidateLevel.SMTP was returned, that means a successful connection was made to the mail server, but for some reason it was rejected. The email address is probably bad.

What's new in version 3.0

New Multi-Threaded MailboxChecker Class
Probably the biggest feature added to aspNetMX is the MailboxChecker class. This is a multithread class, loaded with configurable options, to check millions of email addresses. The MailboxChecker class will check email addresses all the way to the mailbox level, in a mult-threaded environment, with built in throttling. If you need to validate 10,000 emails or 1,000,000 emails, this is the class for you.

New Licensing System
Starting with version 3.0, aspNetMX now uses a simple license key system. We've heard developers feedback, to get away from license files. Now, using a simple key, you can enable aspNetMX in your applications. When moving from server to server, you no longer have to worry about license files being left behind.

Extended the EmailValidator Web Validation Control
We've extended this validation control Additional new features allow you to check the last level of validation achieved, along with ignoring empty email addresses, and accessing the in-memory log.

Move Syntax Validation Options
In previous versions of aspNetMX, the email address syntax was simply checked by using complicated regular expressions. This allowed for edge case email address formats to be incorrectly discarded. New options allow you to select which set of rules you want to implement when syntactically validating email addresses.

Timed Validation Options
aspNetMX now includes the option for timed validation. This option allows the developer to attempt to validate the email address in a set number of milliseconds (configurable by the developer). No longer do you have to wait for unresponsive DNS or Mail servers before you get a result back.

aspNetMX now includes the option to check for greylisting validation. Mail servers that implement greylisting can be flagged, and then marked for later follow-up.

Proxy Server Functionality
aspNetMX now has support for proxy servers. Configure the MXProxy class for email validation from behing SOCKS proxies.

Better COM/ASP Support
aspNetMX now supports COM and classic ASP environments. Wrapper classes make it easier to call methods, that normally wouldn't be available to the COM world.

What's new in version 2.0
aspNetMX is even more powerful than before. Check out some of these new features in 2.0.

New Events
Get even better control with your application with the new events in aspNetMX. Some of these events include the OnServerResponse, OnError, an OnLog event.

The new OnServerResponse allows you to inspect the SMTP response, line by line, word for word, so you can exactly see why an email address is rejected.

The new OnError event is raised every time an internal exception is thrown. Now you can control if you want that exception suppressed, or thrown.

The new OnLog event is raised every time a new log entry is created. Record entries to a central database, your own custom files, or create your own notification program.

New MX Checking Features
aspNetMX has even more powerful DNS MX record checking features. We’ve added the capability to recurse subdomains for the MX records. This helps when the recipient has mis-typed their domain name. aspNetMX also checks the literal domain names, so it validates SMTP servers found at the 'A' record of the domain. Another added bonus is the DnsRetries and DnsRetryPause features. aspNetMX will now retry DNS queries. Because of aspNetMX’s speed, we found it was overloading DNS servers. aspNetMX now has the capability to retry queries, and even allow you to specify a pause interval in milliseconds to give your DNS server time to query for MX records.

Better Logging, Debugging and Exception Handling
aspNetMX now logs additional debug statements to the validation log for easier troubleshooting. If exceptions are raised, they can now be trapped in the OnError event. If all exceptions want to be ignored, simply set the new ThrowExcpetion property to false. aspNetMX also raises specific exceptions during the validation process. For example DnsExceptions are raised during any DNS query errors.

A Word about Email Validation
Email validation is a tricky process. aspNetMX has made this process incredibly simple and powerful. The only correct way to verify an email address exists is to send a mailbox an email and see if you receive a bounce back email or NDR (Non-Deliverable Receipt). aspNetMX goes as far as possible in attempting to validate email addresses WITHOUT sending an actual email.

There are a couple of issues to be aware of when validating email addresses at the MXValidateLevel.Mailbox level.

Positive Validation when a Mailbox doesn't exist
Some mail servers always return a positive response that a mailbox exists, and it is only until an email is sent to a mailbox, that the server responds with a negative response saying a mailbox does not exist. Microsoft's exchange server is notorious for doing this. However, we have optimized aspNetMX to help with this situation, and return faster results against these known servers.

MXValidateLevel.Mailbox can be a Time Intensive Process
To better explain what happens under the covers when an email addresses is tested to Mailbox level, the following steps occur:

  1. The email addresses is syntactically checked.
  2. If the email address is valid, a DNS Lookup for MX Records is made. This involves network calls to DNS Servers to see if MX Records exist. If the binary MX Records exist, and are returned to aspNetMX, aspNetMX turns the records into a usable form.
  3. If the MX Records return the names of the Mail Servers, and not the IP addresses of the mail servers, another DNS call is made to lookup the actual IP addresses.
  4. Once the IP addresses have been determined, another network call is made, this time to the email address's SMTP server. If the mail server is not responding, and there are fail over MX Records, aspNetMX will resolve each of the additional MX Records to IP addresses and then attempt to make a successful SMTP connection.
  5. Once a SMTP session has been established, standard SMTP commands are issued against the mail sever to determine if a mailbox exists for the email address. To protect against email harvesting, some mail servers will always return a positive response, saying a mailbox exists, when in fact, it doesn't. Also, a DNS Server or SMTP server may be down at the very instance you are attempting to validate an email address. Thus aspNetMX could accidentally mark that email address as not valid, when in fact it is. It's recommended that you test failed email addresses a couple of times, at different times, to verify they are in fact bad.


aspNetMX has been highly optimized, unfortunately, most of the time-intensive issues that affect email validation are outside of the control of aspNetMX. These include the across-the-internet or across-the-network DNS lookups, and the across-the-internet SMTP calls. Depending upon your network speed, and the remote SMTP server, the whole process may be completed in a few milliseconds, however, we've seen it take as long as 60 seconds. To help with this, aspNetMX utilizes a number of built-in higher-performance techniques. Check out aspNetMX's High Performance Features.




Thanks so much - this component (and its support) is truly exceptional! "

R. Ifferte

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