Hi @Ken Dicken ,
Welcome to our forum!
What's the version of your Outlook? (File > Office Account > About Outlook). Please make sure you have upgraded your Outlook to the latest version.
Does this issue occur with all sent emails or some specific emails? If some specific emails, do they have something in common? Just like email too large or with large attachments?
In order to further confirm if the issue is related to Outlook desktop client, it's suggested that you could log in to you web mail and send the same email to check if there're any difference. If everything is OK on web mail, please try the below troubleshooting:
- Considering the impact of some add ins, It is suggested that you try to start outlook in safe mode(win+R>type: outlook /safe) to check whether it works normally.
- If this is still the issue in safe mode, it is suggested that you could try to create a new profile (Control Panel>Mail>Show Profiles>add) and add the account for testing to check if there are some differences.
- Considering the impact of some third-party programs on your computer, please try to perform a clean boot for windows and check if the issue still occurs.
- Considering that it would also be affected when the outlook program itself is damaged, it is recommended that you try to fix the Office application.
Hope to help you!
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