MELMS Pro   
http://www.pawsoft.com

MELMS Pro is a complete email list management and mailing system. Features include: automated subscriber/unsubscriber management, email notification for new subscribers, compose and send emails to subscribers, help system including tutorials and much more! MELMS Pro has been designed to be as easy to use as possible while providing all the functionality you need to manage your mailing lists effectively. A free trial is available.

POP3 OCX   
http://www.vb4all.net

The POP3 OCX component is an advanced Active-X control which can be embedded into any Active-X compatible environment, and used to check pop3 servers for email. With the control you can enumerate the properties of received emails for validation or data retrieval. The component has a full series of properties and methods that can be used to interact with email.

MailBee SMTP   
http://www.afterlogic.com

MailBee SMTP is a powerful and easy to use COM object which enables ASP and Windows applications to create, send and queue mail to SMTP servers. Secure authentication, email validation, correct MIME composer, multiple attachments, and much more. Can be used in conjunction with SSL, SMIME, POP3 and IMAP4 components. Royalty-free distribution.

MailBee Objects   
http://www.afterlogic.com

MailBee Objects is a set of powerful and easy-to-use COM objects sending, receiving and managing mail on SMTP, POP3 and IMAP4 servers. Smart and fast MIME parser, HTML and S/MIME mails, HTML mail safety (using MessageCensor component), ESMTP, SMTP queue, secure authentication, SSL/TLS (using SSL plugin), international charsets, email validation, multiple attachments, search for new/unread mails and mailbox management (IMAP4 only). Royalty-free distribution.

Pivo Email Validator Component   
http://www.pivo.com

Having problems with the email addresses in your mailing list?Are you tired of getting bounce backs every time you perform a mailing? Email Validator will solve your email validation problems. Email Validator is an assembly that requires the Microsoft .NET framework to run. It is used to validate email addresses at different levels. Email Validator does not have a GUI front end, it is a server component that can only be accessed programmatically. Email Validator can be used on signup forms or it can validate huge lists of email addresses from one address to million. Email Validator validates email addresses at four different levels. Syntax, Domain, SMTP, and Mailbox levels. To validate an email address, simply create the EmailValidator object, pass it the email address and the level of validation to check, and Email Validator will do the rest. For some code examples on how to use Email Validator, click here. Email Validator 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 Email Validator.