library(RDCOMClient)
## init com api
OutApp <- COMCreate("Outlook.Application")
## create an email 
outMail = OutApp$CreateItem(0)
## configure  email parameter 
outMail[["To"]] = "reciever@mail.com"
outMail[["subject"]] = "subject"
# There are two ways you can write for mail body
# First:text
# outMail[["body"]] = 
# "Dear reciever,
#                      
# Please see attached.
# 
# 
# Best regards,
# Sender"

# Second:html text
body <- 
'
<p>Dear reciever,</p>
<p>Please see attached.</p>
<br>
<br>
<p>Best regards,
<p>Sender</p>'

outMail[["HTMLbody"]] = body

# attachment
outMail[["Attachments"]]$Add("path of your attachment")
## send it                     
outMail$Send()