Hi Naveen,

> Kindly suggest a suitable/compatible open source MIME
> library to use for attaching files when using curl's SMTP
> client for sending mails using TLS.

I don't know of any MIME libraries that will do this for you but I have
written my own email generation (for using with libcurl's SMTP) and email
parsing (when receiving emails via libcurl's POP3) and it is relevantly easy
to do this yourself. You will need a base64 encoding function and a
quoted-printable encoding function (if you want to encode your text
content).

Typically the SMTP message consists of a set of headers, a blank line and a
body. Libcurl adds the necessary EOB terminator that is required by the
server to terminate the message so you don't need to add that.

Your header will need to:

* Set the Content-Type to multipart/mixed making sure to include a boundary
specifier. I use a 16 random character base64 string.
* Set the Mime-Version header to 1.0.

The body of the message will then include:

* Optional pre-amble text - which might be "This is a multi-part message in
MIME format.".
* A number of sub-messages. One for the actual email content and one for
each file attachment. Each sub-message will have their own header, blank
line separator and body. Typically Content-Type and
Content-Transfer-Encoding are included for the email content and
Content-Type, Content-Transfer-Encoding, Content-Description and
Content-Disposition for file attachments. See my example at the end of this
email for details.
* An optional epilogue - which I don't include.

If you want to include plain text and html text (and/or rich text)
alternative context then things get a little more complicated. If you want
to include inline images in your html text then again, things are even more
complicated but I can talk you through these if you need to do this.

Kind Regards

Steve

From: steve_holme_at_hotmail.com
To: user_at_domain.com
Subject: Test Message
Date: Mon, 02 Apr 2012 11:00:00 +0100
Content-Type: multipart/mixed; boundary="pj+EhsWuSQJxx7pr"
Mime-version: 1.0

This is a multi-part message in MIME format.

--pj+EhsWuSQJxx7pr
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable

Hello

--pj+EhsWuSQJxx7pr
Content-Type: application/octet-stream;
        name="Test.txt"
Content-Transfer-Encoding: base64
Content-Description: Test.txt
Content-Disposition: attachment;
        filename="Test.txt"; size=400;
        creation-date="Mon, 02 Apr 2012 10:00:00 GMT";
        modification-date="Mon, 02 Apr 2012 10:00:00 GMT"

[base64 encoding text split across multiple lines, each being 76 characters
long]

--pj+EhsWuSQJxx7pr--

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Received on 2012-04-02