If you are using the “New” Outlook, switch back to the “Old” Outlook to allow for email actions to function properly.

I’m using “Old” outlook.

Hi Reinstall the Office 365 software and it works. I had same issue today and this solved it.

@Koushik.G1  i have outlook installed on my machine, but when i use send mail:outlook i get the same error. Do you know why it could be?

I use microsoft365,  version 2408

@Aaron.Gleason hi, what does new or old outlook mean? What should I check to be able to send email via outlook? I use microsoft 365, version 2408

If you're using the stand-alone Outlook application, in the upper right corner may be a switch for New or Old (Classic) Outlook. New Outlook doesn't support sending mail through the Outlook connector, but Classic Outlook does. 

@Aaron.Gleason  outlook(classic) is written when i search from windows:search, but i get that email error. Idk what to do

If there is File bar in outlook, its old outlook as i searched. So its old outlook but i get error

Only thing to do is a repair of your Office installation. 

https://support.microsoft.com/en-us/office/repair-an-office-application-7821d4b6-7c1d-4205-aa0e-a6b40c5bb88b#ID0EBF=Windows_11

Hello Semih, you have office 365 on ur machine which you can uninstall and reinstall. this would do the trick. If u are using new version of office then switch to older version. Make sure u update the email packages as well.