Transferring mail to the cloud, how to do it correctly?

Question

Email

I welcome the respected community, I ask you to suggest how best to move mail from a physical server (sendmail) to the cloud.
How best to implement so that everything goes as smoothly as possible for users. Physically, the sendmeil must remain for sending mail from intra-office self-written utilities.
Thanks for the advice!

Answer 1

we create copies of boxes in the cloud,
then we synchronize with the imapsync utility and then switch users

Answer 2

intra-office self-written tools are tied to the domain that sendmeil is currently serving .. these tools send and receive mail for this domain, how to deal with them? What is the best way to organize redirection?