Hi @Kerrie Lindh
Welcome to our forum!
It seems that you have set too many accounts in the same profile. Maybe you may consider creating two or more profiles and add corresponding accounts to manage them, more information: Create an Outlook profile - Microsoft Support.
If you find it a bit of a hassle to change your profiles, as a workaround, it is suggested please use both the web and the client to log in to manage your accounts and then send emails from corresponding accounts.
If you are more willing to manage your accounts in the same profile in Outlook Desktop Client, you may remove all accounts except primary email account, re-add them and do the same test to see if the issue persists.
Hope it helps!
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