HTML-Email with inline attachments and non-inline attachments

Question

What is the correct way to create a HTML-Email with inline attachments and non-inline attachments?

In addition please tell me what Content-Type to use with only inli

Answer 1

Images

Yes, it is correct approach to use multipart/related content type. Here is an example (please note 'Content-Type' and 'Content-Disposition' values):

Example source and detailed info

Here are samples you've requested:

1. Email with inline only attachments
2. Email with non-inline only attachments
3. Email with inline and non-inline attachments

Sample 1: inline only

Subject: Test 01: inline only
To: Renat Gilmanov
Content-Type: multipart/related; boundary=089e0149bb0ea4e55c051712afb5

--089e0149bb0ea4e55c051712afb5
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">Lorem ipsum dolor sit amet, consectetur adipiscing elit. P=
ellentesque odio urna, bibendum eu ultricies in, dignissim in magna. Vivamu=
s risus justo, viverra sed dapibus eu, laoreet eget erat. Sed pretium a urn=
a id pulvinar.<br><br><img src=3D"cid:ii_ia6yo3z92_14d962f8450cc6f1" height=
=3D"218" width=3D"320"><br>=E2=80=8B<br>Cras eu velit ac purus feugiat impe=
rdiet nec sit amet ipsum. Praesent gravida lobortis justo, nec tristique ve=
lit sagittis finibus. Suspendisse porta ante id diam varius, in cursus ante=
 luctus. Aenean a mollis mi. Pellentesque accumsan lacus sed erat vulputate=
, et semper tellus condimentum.<br><br>Best regards<br></div>

--089e0149bb0ea4e55c051712afb5
Content-Type: image/png; name="test-01.png"
Content-Disposition: inline; filename="test-01.png"
Content-Transfer-Encoding: base64
Content-ID: <ii_ia6yo3z92_14d962f8450cc6f1>
X-Attachment-Id: ii_ia6yo3z92_14d962f8450cc6f1

iVBORw0KGgoAAAANSUhEUgAAAUAAAADaCAYAAADXGps7AAAABHNCSVQICAgIfAhkiAAAAAlwSFlz
AAALewAAC3sBSRnwgAAAABl0RVh0U29mdHdhcmUAd3d3Lmlua3NjYXBlLm9yZ5vuPBoAAALnSURB
...
QCDLAIEsAwSyDBDIMkAgywCBLAMEsgwQyDJAIMsAgSwDBLIMEMgyQCDLAIEsAwSyDBDIMkAg6wK+
4gU280YtuwAAAABJRU5ErkJggg==
--089e0149bb0ea4e55c051712afb5--

Sample 2: only attachments

Subject: Test 02: only attachments
To: Renat Gilmanov 
Content-Type: multipart/mixed; boundary=047d7b41cc5c82ae5d051712c40c

--047d7b41cc5c82ae5d051712c40c
Content-Type: text/plain; charset=UTF-8

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque
odio urna, bibendum eu ultricies in, dignissim in magna. Vivamus risus
justo, viverra sed dapibus eu, laoreet eget erat. Sed pretium a urna
id pulvinar.

Cras eu velit ac purus feugiat imperdiet nec sit amet ipsum. Praesent
gravida lobortis justo, nec tristique velit sagittis finibus.
Suspendisse porta ante id diam varius, in cursus ante luctus. Aenean a
mollis mi. Pellentesque accumsan lacus sed erat vulputate, et semper
tellus condimentum.

Best regards

--047d7b41cc5c82ae5d051712c40c
Content-Type: image/png; name="test-02.png"
Content-Disposition: attachment; filename="test-02.png"
Content-Transfer-Encoding: base64
X-Attachment-Id: f_ia6yvl4b0

iVBORw0KGgoAAAANSUhEUgAAAUAAAADaCAYAAADXGps7AAAABHNCSVQICAgIfAhkiAAAAAlwSFlz
AAALewAAC3sBSRnwgAAAABl0RVh0U29mdHdhcmUAd3d3Lmlua3NjYXBlLm9yZ5vuPBoAAALnSURB
...
gECWAQJZBghkGSCQZYBAlgECWQYIZBkgkGWAQJYBAlkGCGQZIJBlgECWAQJZBghkGSCQZYBA1gWV
ywTWDU1tpwAAAABJRU5ErkJggg==
--047d7b41cc5c82ae5d051712c40c--

Sample 3: inline and attachments

Subject: Test 03: inline and attachments
To: Renat Gilmanov
Content-Type: multipart/mixed; boundary=001a11c24d809f1525051712cc78

--001a11c24d809f1525051712cc78
Content-Type: multipart/related; boundary=001a11c24d809f1523051712cc77

--001a11c24d809f1523051712cc77
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: quoted-printable

<div dir=3D"ltr">Lorem ipsum dolor sit amet, consectetur adipiscing elit. P=
ellentesque odio urna, bibendum eu ultricies in, dignissim in magna. Vivamu=
s risus justo, viverra sed dapibus eu, laoreet eget erat. Sed pretium a urn=
a id pulvinar.<br><br><img src=3D"cid:ii_ia6yyemg0_14d9636d8ac7a587" height=
=3D"218" width=3D"320"><br>=E2=80=8B<br>Cras eu velit ac purus feugiat impe=
rdiet nec sit amet ipsum. Praesent gravida lobortis justo, nec tristique ve=
lit sagittis finibus. Suspendisse porta ante id diam varius, in cursus ante=
 luctus. Aenean a mollis mi. Pellentesque accumsan lacus sed erat vulputate=
, et semper tellus condimentum.<br><br>Best regards</div>

--001a11c24d809f1523051712cc77
Content-Type: image/png; name="test-01.png"
Content-Disposition: inline; filename="test-01.png"
Content-Transfer-Encoding: base64
Content-ID: <ii_ia6yyemg0_14d9636d8ac7a587>
X-Attachment-Id: ii_ia6yyemg0_14d9636d8ac7a587

iVBORw0KGgoAAAANSUhEUgAAAUAAAADaCAYAAADXGps7AAAABHNCSVQICAgIfAhkiAAAAAlwSFlz
AAALewAAC3sBSRnwgAAAABl0RVh0U29mdHdhcmUAd3d3Lmlua3NjYXBlLm9yZ5vuPBoAAALnSURB
...
QCDLAIEsAwSyDBDIMkAgywCBLAMEsgwQyDJAIMsAgSwDBLIMEMgyQCDLAIEsAwSyDBDIMkAg6wK+
4gU280YtuwAAAABJRU5ErkJggg==
--001a11c24d809f1523051712cc77--
--001a11c24d809f1525051712cc78
Content-Type: image/png; name="test-02.png"
Content-Disposition: attachment; filename="test-02.png"
Content-Transfer-Encoding: base64
X-Attachment-Id: f_ia6yymei1

iVBORw0KGgoAAAANSUhEUgAAAUAAAADaCAYAAADXGps7AAAABHNCSVQICAgIfAhkiAAAAAlwSFlz
AAALewAAC3sBSRnwgAAAABl0RVh0U29mdHdhcmUAd3d3Lmlua3NjYXBlLm9yZ5vuPBoAAALnSURB
...
gECWAQJZBghkGSCQZYBAlgECWQYIZBkgkGWAQJYBAlkGCGQZIJBlgECWAQJZBghkGSCQZYBA1gWV
ywTWDU1tpwAAAABJRU5ErkJggg==
--001a11c24d809f1525051712cc78--

Quick summary

1. Inline only attachments: use multipart/related
2. Non-inline only attachments: use multipart/mixed
3. Inline and non-inline attachments use multipart/mixed and multipart/related

Update

Here is a very interesting article: Using Images in HTML Email