bash_mail.sh

#!/bin/bash

# Function to connect to SMTP and send mail to it
# returns:
# 0 - SUCCESS
# 1 - FAILURE: unable to complete session to DATA command
# 2 - FAILURE: problems after DATA command (server did not enqueue the message)
function bash_mail(){
  # Default configuration
  # Can be overridden by ARGV in order: TO, SUBJECT, MESSAGE, FROM, SERVER
  TO=${1:-'me@example.com'}
  SUBJECT=${2:-"Probleem ${HOSTNAME}"}
  MESSAGE=${3:-'Panic! Come to rescue.'}
  FROM=${4:-"root@${HOSTNAME}"}
  SERVER=${5:-'mail.example.com'}
  

  # start a subshell to aquire own set of filedescriptors
  # Note! echo output must be redirected to 0, else it defaults to 1
  (

    # Compose all commands in an array
    # starts from 1 to be in sync with reply codes (see below)
    cmds=(
      "HELO ${HOSTNAME}\r\n"
      "MAIL FROM: $FROM\r\n"
      "RCPT TO: $TO\r\n"
      "DATA\r\n"
      "From: $FROM\r\nTo: $TO\r\nSubject: $SUBJECT\r\n\r\n${MESSAGE}\r\n.\r\n" 
      "QUIT\r\n"
    )

    # expected reply codes in order
    codes=( 220 250 250 250 354 250 )

    # iterate over all commands
    for (( i = 0; i < ${#cmds[*]}; i++ ))
    do

      # read input
      read code msg <&0

      # check that server replied with correct success code
      if [ $code = ${codes[$i]} ]
      then
        echo -en ${cmds[$i]} >&0
      else
        break
      fi
    done
    
    # workaround to deliver $i outside the subshell
    exit $i
  )<>/dev/tcp/$SERVER/25
  
  # recatch the $i
  i=$?

  # result codes based on where the loop broke off
  results=( [5]=2 [6]=0 )
  # if defined, return from results array, else return 1
  return ${results[$i]:-1}
}