Outlook 365 file attachment option auto-applies CSV column headers - mule

Question

I need to develop an integration using Mule which will create a *.csv file without headers, and email the file content as email attachment using Outlook 365.
Using DataWeave 2.0, I defined output application/csv header = false to create required CSV content without headers. Output of the DataWeave script is correct, which I checked in application logs and also by writing to local file system.
In the next step, I am passing this output payload to Outlook 365 using below code (MuleSoft Outlook 365 connector internally uses Outlook mail REST API - https://learn.microsoft.com/en-us/graph/api/resources/mail-api-overview?view=graph-rest-1.0):
%dw 2.0
import * from dw::core::Binaries
output application/json
---
{
"message": {
"subject": "Summary-" ++ now() as String {
"format": "yyyyMMdd"
},
"body": {
"contentType": "Text",
"content": "Please find attached summary"
},
"toRecipients": [{
"emailAddress": {
"address": p('outlook.toRecipients')
}
}],
"attachments": [{
"#odata.type": "#microsoft.graph.fileAttachment",
"name": "service-data.csv",
"contentType": "application/csv",
"contentBytes": toBase64(write(payload, "application/csv"))
}]
},
"saveToSentItems": "true"
}
Receiver of this email finds column headers created in the attached file, example:
column_0,column_1,column_2,column_3,column_4,column_5,column_6,column_7,column_8,column_9,column_10,column_11,column_12,column_13,column_14,column_15,column_16,column_17,column_18
,SDEN1001107GR,Dense 7.3N 100mm,Days,0,,Blank,,,,,,,,,,,,
I debugged this, and looks like Outlook 365 connector automatically adds column header 'column_X' if not defined. But, the requirement is not to include headers in the file attachment.
Could anybody please help how to ignore the column headers in email attachment?
Sample request payload:
[
{
"Code": "SDEN1001107GR",
"UnitUsagesUsage": "Days",
"Group": "Blank",
"Category": "A",
"Description": "Dense 100mm",
"Rate": "0"
}
]

Answer 1

The issue seems to be that DataWeave -not the connector- is receiving the header=false property as a reader property rather than a writer property. For example in the read() function or in the outputMimeType attribute of a source or operation. Reader properties apply to the input of the script.
You need to use as a writer property instead for the property to be applied to the output.
In the write() function you add writer properties as an additional parameter:
write(payload, "application/csv", {header: false})