Blat is a very small utility that can send messages through the SMTP protocol. It is designed primarily for experienced users and system administrators, as it is managed through a command line. You can view the list of commands and instructions for use in the Docs directory.
E-mails can be sent either manually or to automate the process: you just need to create a simple bat-file where you can write all the necessary instructions, you can use a text document as a base with addresses, among other things, the program can add files to the e-mails as attachments.
Since the program is completely free and distributed under the GPL license, it can be used in your projects, the source code is available to programmers on the developer's website.