Hi @Rob ,
According to your description, everything can work fine on your desktop client and this issue only happen to your Outlook mobile app. So, seems we can infer that this is an Outlook for Android app issue. It is suggested for you to check if there is any specific settings on the phone side.
By the way, please kindly understand that the Outlook tag here we mainly focus on general issues about Outlook desktop client and know little about Outlook for mobile. If you want to get more information about Outlook for Android, please post a new thread to the dedicated forum for Outlook for Android.
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