I was about to send an image inline in an email using the venerable MIME standard, when I remembered that many clients don't handle that very well.
So I created a test email to see how they do.
The email is very simple - some text, an inline image, and some more text. Here is a copy, if you want to test your favourite client.
My email client shows it like this:
Here are the results:
|Client||Shows image inline||Shows text after image||Screenshot|
|Gmail||❌ at bottom||✓||image|
|Office 365 Outlook||❌ at top||❌ hidden as attachment||image|
|Outlook iPhone||✓||❌ hidden as attachment||image|
|Protonmail||❌ as attachment at bottom||✓||image|
|Tutanota||❌ as attachment at top||❌ hidden as attachment||image|
|K9 Android||❌ as attachment at bottom||✓||image|
So what I remembered was not wrong. Most email clients suck at MIME.
The Outlook app on the iPhone gets an extra half mark subtracted for showing an exceedingly ridiculous amount of vertical white space.
Which is not surprising, the relevant RFC is from 1996.