Options for uploading files for attachments. When sending emails with the API that require attachments first upload each attachment. Then use the returned attachment ID in your
SendEmailOptions when sending an email. This way you can use attachments multiple times once they have been uploaded.
|base64Contents||String||Base64 encoded string of file contents. Typically this means reading the bytes or string content of a file and then converting that to a base64 encoded string.||[optional]|
|contentType||String||Optional contentType for file. For instance `application/pdf`||[optional]|
|filename||String||Optional filename to save upload with. Will be the name that is shown in email clients||[optional]|