Keep in mind VZ MMS (or any mobile or email provider) could consider it spam too and limit or block it if too many emails are being sent at once.
If you haven't done it, I would suggest you work on motion settings to knock out almost all false triggers. BI sending 12 emails or MMS at once will probably redflag most providers.
When I first started they were sporadic or late due to sending so many that ended up being false OR I really didn't need the alert (live every car driving by), but as I dialed in my system, the results are almost instantaneous and consistent now.
As I have got more comfortable with my system and its capabilities, I have configured it to only send me text messages for violations of my "personal space".
If you are having text messages go to more than one person at once, then in the alerts, add a break time in between each email/text Alert being sent and see if that gets the others through. BI sends them fast, so the email or mobile provider could be thinking it is a spamming event. Or if you have two cameras that basically trigger at the same time, add a break time first. Usually 1000 ms is enough for providers to not consider it spam.
I have found that generally the email provider and mobile provider play better if there are not lots of messages going out in rapid fire as that is probably what is kicking in the "spam".
I don't need a text every time a vehicle drives by or someone walks on the public sidewalk LOL.