Quota Planning - Inbox - Example Calculations

Emails originating internally to your Exchange organization

500 Exchange Mailboxes x 42 emails sent per day = 21,000 total emails sent per day
21,000 total emails sent per day x 20% with a qualifying attachment = 4,200 Incident Reports per day
4,200 Incident Reports per day x 100 KB average message with attachment size = ~410 MB per day

~410 MB per day x 30-day work queue capacity = ~12 GB

Emails originating externally to your Exchange organization

50,000 emails originating externally arrive per day x 20% with a qualifying attachment = 10,000 Incident Reports per day
10,000 Incident Reports per day x 100 KB average message-with-attachment size = ~980 MB per day

~980 MB per day x 30-day work queue capacity = ~29 GB

Set ProhibitSendReceiveQuota to at least ~41 GB (~12 GB + ~29 GB)