Move mail to another server (cpanel)

We are currently hosting with Future Hosting and we have a dedicated server with 140 email accounts and a proprietary PHP application running. We want to separate the email accounts and remove them all from this server and from another type of server. The idea is to ensure that the email never falls when the PHP server crashes.

Email consumes 200 Gb, so we need something like 300 Gb to start, give or receive. With room to add later.

To achieve this with Future Hosting, it is required to buy another dedicated server, but I do not want to pay the same price, it does not seem reasonable.

Any recommendations on what type of hosting will handle email of this size with a low monthly cost? Backup copies are required.

Thank you!