cURL Mail Attachment (Imagines, .exe file, .rar/.zip files)

Question

I was wondering if I can send different type of files to an email as an attachments. I only know how to send a text file using cUrl. Could someone give me some examples of how can I accomplish my goal ?

This is what I have so far :

curl --url "smtps://smtp.gmail.com:465" --mail-from "mail.gaming@gmail.com" --mail-rcpt "mail2@gmail.com" --ssl --user "mail@gmail.com:password" --upload-file "C:\Folder\File.txt"

Thank you for all the effort !

Answer 1

You can use multipart/mixed content to transmit your text body and each of your binary attachments.

Here is a template of file you could use to display a text file and attach 2 binary files :

From: Some Name <sender@gmail.com>
To: Some Name <receiver@gmail.com>
Subject: example of mail
Reply-To: Some Name <sender@gmail.com>
Cc: 
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary="MULTIPART-MIXED-BOUNDARY"

--MULTIPART-MIXED-BOUNDARY
Content-Type: multipart/alternative; boundary="MULTIPART-ALTERNATIVE-BOUNDARY"

--MULTIPART-ALTERNATIVE-BOUNDARY
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64
Content-Disposition: inline

This is an email example. This is text/plain content inside the mail.
--MULTIPART-ALTERNATIVE-BOUNDARY--
--MULTIPART-MIXED-BOUNDARY
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="file.rar"
<HERE BASE64 ENCODED RAR FILE>


--MULTIPART-MIXED-BOUNDARY
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="file.zip"
<HERE BASE64 ENCODED ZIP FILE>


--MULTIPART-MIXED-BOUNDARY--

Note that the binary files are encoded in base64 and are transmitted as attachment.
Here is an example of building this file and send the email with a bash script :

#!/bin/bash

rtmp_url="smtp://smtp.gmail.com:587"
rtmp_from="sender@gmail.com"
rtmp_to="receiver@gmail.com"
rtmp_credentials="sender@gmail.com:secretpassword"

file_upload="data.txt"

echo "From: Some Name <$rtmp_from>
To: Some Name <$rtmp_to>
Subject: example of mail
Reply-To: Some Name <$rtmp_from>
Cc: 
MIME-Version: 1.0
Content-Type: multipart/mixed; boundary=\"MULTIPART-MIXED-BOUNDARY\"

--MULTIPART-MIXED-BOUNDARY
Content-Type: multipart/alternative; boundary=\"MULTIPART-ALTERNATIVE-BOUNDARY\"

--MULTIPART-ALTERNATIVE-BOUNDARY
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64
Content-Disposition: inline

This is an email example. This is text/plain content inside the mail.
--MULTIPART-ALTERNATIVE-BOUNDARY--
--MULTIPART-MIXED-BOUNDARY
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=\"file.rar\"" > "$file_upload"

# convert file.rar to base64 and append to the upload file
cat file.rar | base64 >> "$file_upload"

echo "--MULTIPART-MIXED-BOUNDARY
Content-Type: application/octet-stream
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename=\"file.zip\"" >> "$file_upload"

# convert file.zip to base64 and append to the upload file
cat file.zip | base64 >> "$file_upload"

# end of uploaded file
echo "--MULTIPART-MIXED-BOUNDARY--" >> "$file_upload"

# send email
echo "sending ...."
curl -s "$rtmp_url" \
     --mail-from "$rtmp_from" \
     --mail-rcpt "$rtmp_to" \
     --ssl -u "$rtmp_credentials" \
     -T "$file_upload" -k --anyauth
res=$?
if test "$res" != "0"; then
   echo "sending failed with: $res"
else
    echo "OK"
fi

The received email will have the inline text/plain document and both of attachment document of type application/octet-stream :