Questions regarding a pilot to Office 365 from an On-Prem Lotus Domino

Hello experts,

we're about to start a pilot as part of planning a migration to Office 365 for a customer which is currently using an On-Prem Lotus Domino. We will be piloting just a handful of the users on the On-Prem Lotus Domino and this will be our first migration to Office 365 from an On-Prem Lotus Domino.

We have a clear understanding of all the DNS settings we need to have in place in order to start the pilot as we set up Hybrid other times in the past.

I would like to check with you if our plan below makes sense to you and if out of courtesy you could provide additional observations/recommendations:

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1 – MX records will still be pointing back to the On-Prem Lotus Domino and not to Office 365
2 – we'll configure forwarding to ensure that email intended for the pilot users will be forwarded correctly to Office 365 using the onmicrosoft.com domain
3 – we've configured the domain as an Internal Relay (instead of Authoritative) in Office 365 as Exchange Online is not going to have knowledge of all the mailboxes on the On-Prem Lotus Domino
4 – we're planning on using BitTitan to migrate all mailboxes data in Office 365
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In order to make sure that mail flow is working correctly between Office 365 and the On-Prem Lotus Domino, we are planning to:

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1 – set up a connector in order for Office 365 to trust email coming from the On-Prem Lotus Domino. At least initially, most likely we will specify the public IP address of the Internet-facing On-Prem email server as our customer does not currently have a certificate from a third-party trusted CA installed on the On-Prem email server
2 – as we will not be setting up Hybrid, my understanding is that Internal Relay will deliver back to the On-Prem mailboxes using the MX record and that, as a result, a connector in order for Office 365 to deliver email back to the On-Prem Lotus Domino is not strictly needed. Is my understanding correct ?
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Any additional observations/recommendations on this matter will be greatly appreciated.

Thanks and Regards,

Massimiliano