A few days ago I recieved an email from virginmobilemessaging.co.uk with the subject MMS. Attached was a photo, and a message as a plain text file (and another file, presumably some metadata).
Question: how and why did I recieve this by email? 
I assume that a part of the network somewhere decided for some reason that it wasn’t going to deliver the MMS to your device and instead the gateway sent an email. 
This could be that something further in the chain doesn’t support it, or someone decided delivering the MMS was more expensive than sending it by email.
Virgin Mobile has done this for so many years, I remember being sent a picture message to a phone that didn’t support it so I received a plain SMS with I think it was a link to see the picture online?
From what I understand, your carrier doesn’t actually have to deliver incoming SMS or MMS messages to your device by those methods. The work in the industry on RCS, WiFi Calling’s message protocol, and bridging older technology into these standards is quite interesting in this regard.
If you start bridging older point to point standards into something more modern and server-side, things get very interesting when it comes to supporting multiple devices on a single phone number.
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Cool ^^ Even more confusing (for me) was getting a follow up message (another emailed MMS) from the same person saying they were baffled at how they had emailed me - so clearly they had some kind of feedback on how it was delivered.
Slight aside: I feel like this is somewhere Zevvle could do some incredible things by building their own infrastructure.
You don’t have to deliver an SMS as an SMS (excluding certain types of message, think iMessage registration on iOS where the device silently intercepts that message). You could deliver it as RCS, an email, a Push Notification to an app, or a webhook. 
Japanese carriers bridge have been bridging SMS messages into email for years due to SMS’ message size limitations and need for Shift-JIS or Unicode encoding.
Given the state of SMS security and how everything is moving such that Voice over LTE is just fancy SIP calls, it certainly seems like there would be a good appetite and reason to offer an upgrade in security even just for the last hop.
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Carriers have allowed MMSes to email for ages. For an MMS the recipient field is alphanumeric so you are welcome to type an email address in there.
Could it be that their phone had your email in their contacts and they accidentally selected that one when sending?
I had a similar occurrence when I blocked someone that was texting me via iMessage using my email as the recipient, once blocked the chat bubbles turned back green (so it fell back from iMessage to MMS) and their carrier sent it to me via good old email.
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YES. That’s the plan. We do our own billing already, but the next step is in-house call & SMS routing (no need to connect with a host for that). Needs a non-trivial investment of time & money though, and is unlikely to happen this year…
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