Our deliverability lead has also put together some great guides on deliverability best practices — I'll include those links below:
We also have a category dedicated to deliverability on our blog36 that you might find useful, as well! ☺️
It's normal for there to be a temporary deliverability drop right after switching providers — because you’re moving to a different email service provider, mailbox providers will need to re-evaluate how they score your messages. During this re-evaluation period, it’s normal to see open rates temporarily decrease (or increase). The 'Getting Started with Deliverability Success' guide linked above goes over some steps that can help shorten this re-evaluation period!
That said, if you're finding the deliverability issues are persisting, please feel free to reach out to our team at email@example.com (or via the in-app messenger in your account) with a description of this issue. One of our Product Specialists will be able to take a look at your account and help troubleshoot further from there, and connect with our deliverability team if needed ☺️