Send email with R from Gitlab CI

I want to send a customised email from R when running Gitlab CI. My R code works on my computer. However, the same R code run in a Gitlab pipeline failed with the following error:

Sending email to  smtp://smtp.office365.com:587 .
Error in curl_fetch_memory(url, handle = h) : Login denied
Calls: smtp -> curl_fetch_memory
Execution halted
ERROR: Job failed: exit code 1

The same error message occurs using two different R packages, i.e. {emayili} and {blastula}. My guess is that the solution (if a solution exists?) lies in the parameters of the SMTP server of Gitlab... but as a R user this goes beyond my expertise. So my question is:

Does someone know some "magic" to send customised email from R when running a Gitlab CI pipeline?

Here is the code I used for an Outlook account:

My .gitlab-ci.yml file:

image: rocker/tidyverse

test:
   script:
    - Rscript send_message.R

My send_message.R file with the R package {emayili}:

remotes::install_github("datawookie/emayili")
install.packages("magrittr")

library(emayili)
library(magrittr)

email <- envelope()

email <- email %>%
  from("r_user@outlook.com") %>%
  to("john_doe@example.com") %>%
  subject("This is a plain text message!") %>%
  text("Hello! This is a test.")

smtp <- server(host = "smtp.office365.com",
               port = 587,
               username = "r_user@outlook.com",
               password = "**********")

smtp(email)

Or the send_message.R file using the R package {blastula}:

install.packages("blastula")
library(blastula)

## Run manually once to get the outlook_creds file
#create_smtp_creds_file(
  #file = "outlook_creds",
  #user = "r_user@outlook.com",
  #host = "smtp.office365.com",
  #port = 587,
  #use_ssl = TRUE
#)

test_message <- prepare_test_message()

test_message %>%
  smtp_send(
    from = "r_user@outlook.com",
    to = "john_doe@outlook.com",
    subject = "Testing the `smtp_send()` function",
    credentials = creds_file(file = "outlook_creds")
  )