Sending HTML reports inline and as attachment created with knitr
In sendmailR: Send Email Using R

knitr::opts_chunk$set(collapse = TRUE, comment = "#>", fig.width = 7, fig.height = 5, warning = FALSE, message = FALSE)
if (!requireNamespace("rmarkdown", quietly = TRUE) ||
    !requireNamespace("htmltools", quietly = TRUE)) {
  knitr::opts_chunk$set(eval = FALSE, tidy = FALSE)
}

This file shows a typical workflow for knitting .Rmd documents and sending them per E-Mail.

First we have our my_file.Rmd which looks like this:

````{=html}

title: ' ' output: html_document: theme: null highlight: null mathjax: null

Hello everyone,\n

here is a calculation.

2+2 =

``{r echo=FALSE} 2+2``

All the best

````

test.Rmd <- "---
title: '&#32;'
output: 
  html_document:
    theme: null
    highlight: null
    mathjax: null
---

Hello everyone,\n

here is a calculation.

**2+2 =**
\```r
2+2

\```

All the best
"
writeLines(test.Rmd, con = "my_file.Rmd")

Render your rmarkdown file

htmlout <- tempfile(fileext = ".html")

rmarkdown::render(
      input = "my_file.Rmd",
      intermediates_dir = ".",
      output_file = htmlout,
    )

This is the resulting HTML document

unlink("my_file.Rmd")
htmltools::includeHTML(htmlout)

Sending the html file per E-Mail

We can now send the the resulting html file as A) an file attachment or B) inline HTML.

A) File attachment

library(sendmailR)
sendmail(from="from@example.org",
         to="to1@example.org",
         subject="File attachment",
         msg=c(
           mime_part("Hello everyone,\n here is the newest report.\n Bye"),
           mime_part(htmlout, name = "report.html")),
         engine = "debug")

B) Inline HTML

sendmail(from="from@example.org",
       to="to1@example.org",
       subject="Inline HTML",
       msg=mime_part_html(htmlout),
       engine = "debug")