The following vb6 example codes demonstrate how to test email address without specified SMTP server.
Validate Email Address Syntax
Regular expression can be used to validate if an email address is in correct format.
For example: you can use this
pattern to verify if the email address has valid format.
Test Email Address
Even the email address has a valid format, it doesn’t mean the email address is existed in real world. TestEmailAddr method can be used to test if the email address is valid.
How does it work? Firstly, SmtpClient performs a DNS MX record query. If it retrieves the recipient’s local SMTP server successfully, SmtpClient will try to connect to this server. SmtpClient then performs “RCPT TO” command to test if this SMTP server accepts this email address.
Please always pass zero-length string to ServerAddr property except you want to test whether an email address will be accepted by a specified SMTP server.
EASendMail is a SMTP component which supports all operations of SMTP/ESMTP protocols (RFC 821, RFC 822, RFC 2554). Before you can use the following example codes, you should download the EASendMail Installer and install it on your machine at first.
To use EASendMail SMTP ActiveX Object in your project, the first step is “Add reference
of EASendMail to your project”. Please select menu ->
EASendMailObj ActiveX Object, click
OK, the reference will be added
to current project, and you can start to use it to send email in your project.
The following example codes demonstrate testing email address using MX DNS lookup.
In order to run it correctly, please change
recipient value to yours.
To get full sample projects, please download and install EASendMail on your machine.
Private Sub btnSendMail_Click() Dim oSmtp As New EASendMailObjLib.Mail oSmtp.LicenseCode = "TryIt" ' Set your sender email address oSmtp.FromAddr = "email@example.com" ' Add recipient email address oSmtp.AddRecipientEx "firstname.lastname@example.org", 0 ' Do not set SMTP server address oSmtp.ServerAddr = "" MsgBox "start to test email address..." If oSmtp.TestEmailAddr() = 0 Then MsgBox "email address was verified!" Else MsgBox "failed to test email address with the following error:" & oSmtp.GetLastErrDescription() End If End Sub
Firstly, SmtpClient performs a DNS MX record query. If it retrieves the recipient’s local SMTP server successfully, SmtpClient will try to connect to this server. SmtpClient then performs “RCPT TO” command to test if this SMTP server accepts this email address.
Because it totally depends on your networking connection, if your networking connection to the recipient server is bad or your IP address is blocked by the recipient server, test will be failed, but it doesn’t mean this email address is invalid.
Moreover, to prevent email address testing, many email providers accept the recipient address at first no matter if the address is valid or invalid, only after you sent the email data to the server, then the server rejects it if the recipient address is invalid.
Send the email to the recipient without testing. If you don’t get Transport Error and Failure Report in 24 hours, that means the recipient is valid. If you get Failure Report, you should consider to remove this recipient from your mail listing.
Seperate builds of run-time dll for 32 and x64 platform
|Installation Path\Lib\native\x86\EASendMailObj.dll||32 bit|
|Installation Path\Lib\native\x64\EASendMailObj.dll||64 bit|
For VB6, C++, Delphi or other standard exe application, you can distribute EASendMailObj.dll with your application to target machine without COM-registration and installer. To learn more detail, please have a look at Registration-free COM with Manifest File.
For ASP, VBScript, VBA, MS SQL Stored Procedure, you need to install EASendMail on target machine by EASendMail installer, both 32bit/x64 DLL are installed and registered.