C library for sending e-mail (with attachments) from C/C++
...The library can also be used to just create a multipart MIME message body.
Also comes with a command line application (quickmail) for sending mails (mutiple attachments supported) from command line or scripts.
Cross-platform.
Binary packages available for Windows (32-bit and 64-bit).
basE91 is an advanced method for encoding binary data as ASCII characters. It is similar to UUencode or base64, but is more efficient. The overhead produced by basE91 depends on the input data. It amounts at most to 23% and can range down to 14%.