Attachments not visible in Outlook 2016

I recently received an update from Microsoft® Office 2011 on my MacBook Pro laptop to Microsoft Office 2016. Included with that update was the 2016 version of Microsoft Outlook for Mac, though if I click on Outlook from Outlook's menu bar and then select About Outlook, I see the following version information (image):

Version 15.27 (161010)
Product ID: 03109-000-000001
License: Volume License

One annoying issue I've encountered is that I don't see a way to view attachments sent with some messages within Outlook. I can see a paperclip icon to the right of the sender's name in the left pane of the outlook window, which indicates the message has been received with an attachment, but in the right pane where the contents of the window is displayed, there is no indication that the message has an attachment. And, if I double-click on the message to open it in a separate window there is no indication the message has an attachment. The only way I've found to easily gain access to the attachment is to view the message in Outlook Web App in a web browser. In its right pane, I see a "To:" line followed by a "CC:" line and then an "Attachments:" line with the name of the attachment shown. I can click on the attachment name to open of save it.

In Outlook 2016, if I right-click on the first message where I observed this problem and choose View Source, I see the following in the header lines, which indicates the message does indeed have an attachment:

Advanced Mac OS X - Technical and Security Skills
Advanced Mac OS X
Technical and Security Skills
1x1 px

Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: yes

Further down I see the following:

--B_3569333336_1269958454
Content-type: text/plain;
	charset="UTF-8"
Content-transfer-encoding: quoted-printable

Hi Jim,

=20

Here is the updated policy.

When I first noticed the problem, since I saw "Content-type: text/plain;" and found others reporting problems with attachments not being visible when senders send email messages as plain text rather than HTML-formatted messages with Outlook 2016, e.g. Can't see my included attachments in "only text" fomatted mails in Outlook version 16.0.6366.2036, I assumed that was the reason I wasn't seeing the attachment for the message where I first noted the problem. However, I found another message where the attachment was not shown where I saw the following when I viewed the source code for the message:

Content-type: text/html;
	charset="UTF-8"
Content-transfer-encoding: quoted-printable

And for one message where I saw an attachment, I saw the following when viewing the source:

X-Auto-Response-Suppress: DR, OOF, AutoReply
Content-type: multipart/mixed;
	boundary="B_3569334466_1922450282"

> This message is in MIME format. Since your mail reader does not understand
this format, some or all of this message may not be legible.

--B_3569334466_1922450282
Content-type: multipart/alternative;
	boundary="B_3569334466_1870965250"


--B_3569334466_1870965250
Content-type: text/plain;
	charset="UTF-8"
Content-transfer-encoding: quoted-printable

I.e., I saw Content-type: text/plain; yet the attachment appeared. When I checked other messages, I found that PDF attachments were not visible if there was a space in the file name, but were visible if there were no spaces in the file name. E.g., when I scrolled down through the source code for one message where the attachment wasn't visible to the base64 encoding of the attachment, I saw the following before the base64 encoded attachment:

Content-type: application/pdf; name="Prime Cloud Roadshow Flyer_Final_r3.pdf";
 x-mac-type="50444620"
Content-ID: <F727DC342F909F4CB45A95803AD263C5@mail.example.com>
Content-disposition: attachment;
	filename="WESTPrime Cloud Roadshow Flyer_Final_r3.pdf"
Content-transfer-encoding: base64

But after even further checking, I found instances of messages with PDF attachments with spaces in the filenames where the attachment was visible. However, in all of the instances I have found so far, in those cases there were other attachments to the messages, i.e., image files with no spaces in their filenames.

Another method I could use to view attachments, aside from using Outlook Web App (OWA), is to view the source code for a message by right-clicking on it and choosing View Source is to then hit the command-f keys and search for base64. I might see something like the following code:

Udemy - April2516-25off-sitewide120x600
--B_3569343163_920316558
Content-type: image/png; name="powerphplist.png";
 x-mac-type="504E4766"
Content-ID: <660a4bd1cf71c70e62ed630bcd56a706>
Content-disposition: attachment;
	filename="powerphplist.png"
Content-transfer-encoding: base64


iVBORw0KGgoAAAANSUhEUgAAAEYAAAAeCAMAAACmLZgsAAADAFBMVEXYx6fmfGXfnmCchGd3
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l1fkb+5zAcz/or8Ag3ozZFZX3G0AAAAASUVORK5CYII=
--B_3569343163_920316558--

I will see two lines a few lines above the Content-transfer-encoding: base64"; line like the following ones:

--B_3569343163_920316558
Content-type: image/png; name="powerphplist.png";

I.e., there will be two dashes followed by a long list of numbers and then on the line below, the type of file and the name of the file. I can copy the base64-encoded text starting with the first non-blank line below the "Content-transfer-encoding: base64" line down through the line ending with an equal sign, but not including the line immediately after it that has the two dashes with the identifying numbers after it that appeared immediately above the "Content-type" line. E.g., in this case from the line that contains:

iVBORw0KGgoAAAANSUhEUgAAAEYAAAAeCAMAAACmLZgsAAADAFBMVEXYx6fmfGXfnmCchGd3

Down through the following line:

l1fkb+5zAcz/or8Ag3ozZFZX3G0AAAAASUVORK5CYII=

I can then copy and paste that text into a file with a text editor, such as the TextEdit app found in the Applications directory or vi or GNU nano, which can be run in a Terminal window. I can then save the text to a text file, e.g., perhaps powerphplist.b64 in this case. I would use a text editor to ensure that no extraneous formatting information is saved within the file, since I want the contents to be plain text. I can then use the base64 command to decode the contents of the file to produce the original file, in this case powerphplist.png.

$ base64 --decode -i powerphplist.b64 -o powerphplist.png
$

I can specify I want the utility to perform decoding with --decode and supply the input file with the -i option and the output file with the -o option. I can then view the output file in the OS X Preview application, if it is an image file, PDF file, etc. that the program can open and display or use whatever document viewer is appropriate for the file type of the attachment.