Hi @Gt ,
From your desctiption, do you mean you would like to request a read receipt when using Outlook on the Web(OWA) or outlook.live.com?
If this is the case, for outlook.live.com or outlook.com, based on my research, this can only be complished when using Outlook for Windows to send emails from the outlook.com account. See Read receipts in Outlook.com. Then please understand that actually outlook.com is currently not supported in Microsoft Q&A forum, if you have further questions or concerns related to outlook.com, you can ask in here: https://answers.microsoft.com/en-us/outlook_com/forum.
When it comes to the Outlook on the Web(OWA) for Exchange Online or Exchange on-prem like Exchange 2016 or Exchange 2019, in order to request read receipt, you can select the "..." icon at the top of the new message compose pane, choose "Show message options", select "Request a read receipt":
For more details, please refer to: Read receipts in Outlook on the web.
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