使用mailR软件包时，kableExtra HTML表无法正确渲染

Question

我正在尝试使用mailR包通过电子邮件发送HTML表。当我渲染降价文件时，表格如下所示： 但是，当我通过电子邮件发送表格时，表格会失去边界，看起来像这样： 有没有办法确保电子邮件中出现边框？

这是我正在使用的代码。

---
title: "Email Test"
output: html_document
---

## Hello world!

```{r setup, include=FALSE, echo=FALSE}
suppressPackageStartupMessages(library(tidyverse))
suppressPackageStartupMessages(library(kableExtra))

### Table 1:

```{r table1, include=TRUE, echo=FALSE, results='asis'}

head (mtcars, 10) %>% 
  rownames_to_column(var = "car") %>% 
  select (cyl, car, mpg, disp, hp) %>% 
  arrange (cyl) %>% 
  kable (escape = FALSE, 
         align = "clccc") %>% 
  kable_styling(c("bordered")) %>% 
  column_spec(1:5, color = "black") %>% 
  collapse_rows(columns = 1, valign = "middle") 

mailR：

library(rmarkdown)
library(knitr)
rmarkdown::render("Email_Test.Rmd")

library(mailR)

send.mail(from = "my.name@myorg.com",
          to = "your.name@myorg.com",  
          subject = "TEST EMAIL",
          html = TRUE,
          inline = FALSE,
          body = "Email_Test.html",
          authenticate = TRUE,
          smtp = list(host.name = "smtp.office365.com", 
                      port = xxx,
                      user.name = "my.name@myorg.ca", 
                      passwd = "xxxxxxxxxxxxx", 
                      tls = TRUE)
          )