I think that new mail9.ntf included with FP9 has error related with this below
Delegated mail files are refreshed automatically (SPR #RGAU829D4G APARID: LO48407)
If you have delegate access to another user's mail file, that mail file is refreshed automatically in your Notes® client. To enable this feature, upgrade to the Mail9.ntf template provided with the FP9 Client. No notes.ini setting is required for this feature.
I reverted mail desing template which was included in FP8, and there is no errors