Greetings Simon, we will look into the My Inbox response that you received. This is the first time we have been informed of that error message.
To answer your questions:
1) You can send an email with a text alternative to our system, but since all of the clients we support in our test support HTML the text alternative will not be displayed.
Thanks for the early-bird response!
The text-alternative thing is actually fine, as I can test that thoroughly locally. We always declare image sizes too, within the HTML, so I can probably get a representative view of the message.
2) No embedded images are supported in our system, regardless of mime-type. Again we do not allow them for security purposes, if we allowed them someone could potentially release malicious code on our servers.
Obviously security is potentially an issue, although exploits involving JPEG, GIF and PNG are very, very rare.
Given three environmental factors,
1. that the vast majority of email recipients in commercial organisations are unable to collect images from an external server (or have that functionality disabled by their administrators), and
2. that the nature of effective email campaigns means that either embedded or hosted, the smallest images practical are used, and
3. that the well-understood (and equally well-disliked) use of the MS-Word HTML rendering engine in the two most recent versions of Outlook means that email with embedded images, per Outlook, has a much higher chance of being presented correctly to an Outlook-using recipient (and it reduces the spam-score significantly, compared to hosting),
I’d thus suggest there is still a powerful case for enabling testing of messages with embedded images. Even with the necessary size and filetype constraints, it would be very useful.
Obviously, if the client’s campaign is aimed at private individuals, this has less importance, but, for people like ourselves (focused on B2B activities), there is little choice but to embed images.
Obviously too, I can quickly work around this restriction by hosting the images, but it’s not then doing the fundamental thing: testing the actual email I will be sending.
So I’d strongly urge you to consider it. You might even charge a premium price for such a service