When using PostMark and sending attachments, the module fails to get the MimeType properly for some files. In my use case, it was an Excel file with the .xlsx extension. I believe this to be an issue with the application server not finding the correct type. Currently, PostmarkProtocol.cfc has this at the bottom:

It is using getPageContext().getServletContext().getMimeType() to determine the MIME type, which doesn't always seem to work. It returns null instead of the correct type.

There is a function called fileGetMimeType() that we can use instead to determine the correct type.

https://cfdocs.org/filegetmimetype

This seems to return the correct type.

To test, try running something like this:

file = "C:\test\test.xlsx";
writeDump( getPageContext().getServletContext().getMimeType( file ) );
writeDump( fileGetMimeType( file ) );

You will see that the first dump returns null whereas the second returns a type.

For testing, I manually made that change in my copy of PostmarkProtocol.cfc and it was able to send the email with an attachment. When the mime type was null, PostMark was throwing an error saying that the contentType is required.