Using an SMTP library, you can build an app to send emails. However, it typically doesn’t support a function to simply pass the subject, content, and attachment as parameters.
Format of Internet Message Bodies
According to RFC2045, the MIME (Multipurpose Internet Mail Extensions) format is used.
From: ocfox <[email protected]>
To: Test <[email protected]>
Subject: Test Email
MIME-Version: 1.0
Content-Type: multipart/mixed;
boundary=_kuroneko_
This is a simple email header where I use a custom boundary _kuroneko_.
The boundary is used to separate different parts of the email.
Header ...
--_kuroneko_
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Hello, this is the text part.
--_kuroneko_
Attachment
An attachment is a part of the email and can be a file, an image, or anything else you want to send.
If you want to send an EPUB file, you need to add a part to the email like this:
Header ...
--_kuroneko_
Content-Type: application/epub+zip; name="example.epub"
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="example.epub"
UEsDBAoAAA...
--_kuroneko_--
Use any Base64 encoding library to encode the file, combining the pieces together. Then, send them using SMTP.
It’s quite simple, right?