MailChannels will likely catch it and halt it if it’s sent without enough delay. The way they work is they learn your sending patterns (per domain) and they block things that quickly ramp up without being part of a normal pattern. So, for example, the first week I might do a strong delay and have it send over the course of 24h. Maybe you take a couple hours off each time until you’re down to something around 6-12 hours.
Now the reason I say stop at around 6-12 hours delay on it is because you can increase the probability of the newsletter being seen as spam merely due to the content and frequency it hits the same filter at Google (which, let’s face it, is almost always most of the recipients). Much like MailChannels, Google doesn’t like large bursts at once either. So you end up doing yourself and the recipients a favor by introducing a reasonable delay.
Personally, I LOVE this for sending newsletters in an effective way: