Hello @Shaun Yang (Medalsoft) ,
Thanks for reaching Microsoft!
I am able to replicate your issue. I would like to suggest a workaround. You can try using the $search query parameter with the Microsoft Graph API.
For example, you can use the following query to filter by the "to" field:
https://graph.microsoft.com/v1.0/me/mailFolders/SentItems/messages?$search="to:{searchphrase}"
Document reference: https://learn.microsoft.com/en-us/graph/search-query-parameter?tabs=http
Hope this helps.
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