blastula not naming attachments correctly

Question

I'm trying to send an email with an attachment (blastula v0.3.4) Everything's working except my attachments arrive called 'Filename' (no extension) instead of 'my_attachment.html'. The contents of the attachment are correct.

Here's my code:

library(tidyverse)
library(DT)
library(blastula)

output_file_body <- paste0(machine, "output/test_mailer_", Sys.Date(), ".html")

rmarkdown::render(paste0(machine, "R/emailbody.Rmd"),
                  output_file = output_file_body,
                  envir = new.env(globalenv())
)

email <- compose_email(
  body = md("Please see the attached HTML file for details.")
  ) %>%
  add_attachment(file = output_file_body, filename = 'my_attachment.html')  # Attach the HTML file

smtp_send(
  email = email,
  from = "[email protected]",
  to = c(
    "[email protected]",
    "[email protected]",
  ),
  subject = "Test Mailer",
  credentials = creds_file(paste0(machine, "no-reply"))

My .RmD is

---
title: testing
date: "`r Sys.Date()`"
output: 
  html_document:
    number_sections: true  
    center: true
    highlight: tango
    theme: spacelab
---

{r Global options, include=FALSE}
knitr::opts_chunk$set(echo = FALSE, message = FALSE, warning = FALSE)

{r }
iris %>% DT::datatable()