Exchange server 2016 Load

Hello All,

Need your expertise here.

There are 2000 plus internal apps which send emails to internal as well as to external domains and we are planning to route them through DNS Round Robin to load balance the 6 exchange 2016 boxes. We will configure all these 6 exchange boxes as SMTP relay.

Could you please guide me how to calculate the capacity of these exchange boxes? How much SMTP traffic load it can take? Capacity, disk, Size, etc.

Note: We have Hybrid set up. No mailboxes are active on these 6 boxes. All mailboxes are migrated to o365.

Regards,
Sounder