Issue synchronisation of mails

Hi 

i have an issue with synchronisation of mail emails.

I had in the past a mail account to the provider infomaniak.

i have made from outlook a backup of all my mail in a PST file, my Mailbox was an IMAP mailboxe.

When i have configured my domain name to Microsoft365 , new mail were coming so perfect.

I have  monted my Backup PST file and imported all my mail in Outlook 365 at this point all was ok but when i'm looking for one of my old mail i don't find it in my outlook client but if i'm look on the web interface of outlook i can find the mails.

I have in the mailbox property ask to sync all my mails but i don't why it don't sync all mails.

I have compared the weight of the folders and on the sever it's bigger than on my PC.

Someone can help me to force the synch and to have all my mails on my outlook client.

Thx.