Welcome PM,
I understand how frustrating it can be when you are encountering a message sending error in the new Outlook for Windows stating “There was a problem sending this message. Please try again later,” and you would like to know whether this could be a temporary issue.
To make sure we are aligned, please confirm whether you have already tried any steps suggested by other replies in the linked thread above.
In the meantime, you can try the workaround steps:
- Restart the new Outlook app and sign back in to your account.
- Check your internet connection and, if possible, switch to a different network temporarily.
- Try sending a short test email without attachments.
- Verify that your mailbox is not full by checking storage usage in Outlook settings (In Outlook > go to Settings (Gear icon) > Storage
- Temporarily toggle off the new Outlook and test sending from classic Outlook to see if the behavior is the same.
I really hope that the information I gave above was helpful to you. Please feel free to reply below and let me know if you have further concern on this matter.
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