How Exchange Online automatically cares for your public folder mailboxes (via AutoSplit)

tonire To get this right so you are using EWS script to take actions on emails received on PF A "delete & move", PF B "create new item", PF C "create new item", If I get you correctly the issue is with deletion process which made Folder A a giant one but why isn't PF B & C are giants since all of them are having same input "email items" with same size?

one more point have you modified DefaultPublicFolderDeletedItemRetention across the organization (least value is 1 day) or even across that PF A "RetainDeletedItemsFor" (you can specify zero days here) where deletions are taking place to ensure that these items are always purged constantly.

Can you share with me your request in a DM?