Internally, Windows service of MailBee.NET Queue monitors that disk folder, picks up all .EML files other applications submit to it, and sends them out through SMTP server. To feed the pickup folder, you can use any tool capable of producing .EML files, including MailBee.NET Objects and MailBee Objects products.
MailBee.NET Queue supports SMTP-over-SSL, SMTP authentication including NTLM and Integrated Windows Authentication, multi-threaded delivery, and logging all the activities into a file. To configure things, you can use a GUI app or edit the config file directly.
And there is MailBee.NET Queue API. Use any .NET language to tell MailBee.NET Queue to use multiple relay SMTP servers for better throughput, use direct send to destination MX servers in case if the SMTP relay server fails, and much more. For instance, you can limit the number of e-mails the service sends per a single SMTP session, number of simultaneous connections with the server, and so on.
To run MailBee.NET Queue, you need a valid MailBee.NET SMTP license key. A unified MailBee.NET Objects key will work as well.
As the full source code is available, you can also use MailBee.NET Queue as an advanced sample of using MailBee.NET Objects for bulk mail delivery.