I'd like to view the full SMTP headers of a message in my gmail app, but haven't found a way to do so. I've also also tried the Web client, but it displays a tablet-specific view, even when I've checked "request desktop site"
Sadly there's no such option in the official Gmail app.
You can try using a third party mail client with more options such as K-9 Mail: http://k9mail.org/
Just use a browser instead of your Gmail app.
Using Chrome (mobile, 47.0.xxxx.xx) on Android (5.0.2), for example,
Go to gmail.com.
Use the three vertical dot menu at upper-right > request desktop site (not sure this step is necessary, but I did it, and it worked).
Use the gmail menu (three vertically-stacked horizontal bars) to the left, above the main window.
Scroll to the bottom and choose "View Gmail in ... Desktop"
Open the email message for which you'd like header information.
Click Show Original just above the window containing the message body.
The header info will appear.
Well, yes SMTP headers can be seen over the Gmail apps.
- Login to your e-mail account (Which I am sure you are logged in over your Gmail app).
- Click over the email you wish to see headers on.
- On the upper right portion of the message box, you will see a Reply or Reply-to-All button, with a small downward pointing arrow.
- Click the small arrow.
- You will see the message sub-menu, and an option for "Show Original"
- Click "Show Original"
Is that you are trying to do ?