Gmail is facing an issue right now. Some email that is sent to non gmail addresses or emails with attachments is not sending due to some error on google side.
Keep an eye on Google Gmail Status page here : https://www.google.com/appsstatus#hl=en
As we don’t know what the exact problem is we can try some solutions that might help.
How to fix Gmail Oops something went wrong message
To fix this try the following solutions:
1. Reset your network settings
Sometimes when your internet is not working you can reset your Network settings by going to Settings > Network & Internet > Choose Network TroubleShooter option to check and fix any network issues.
2. Try using another Browser to send your emails
Sometimes gmail might not work properly if the latest browser update for chrome or firefox might have broken some code on gmail. So try other browser like Microsoft Edge or Opera.
3. Use an alternative Email for now ( Best solution )
Here are some free alternatives to gmail
If the above solution’s din’t work for you, We can only wait until gmail fixes the issue.
Hope you were able to find the problem that’s making gmail show the Cannot send email error.