If you receive an error message when sending an email, there are a few steps to take in order to troubleshoot the issue:

1. Check the recipient’s address. Make sure you have entered the correct address and that the domain name is spelled correctly.
2. Check your outbox and confirm that your message has been sent. If not, try re-sending it.
3. Check the spelling and content of your email. Make sure there is nothing that would trigger blocked content or spam filters.
4. Check the size of your attachments. The total size of all attachments combined should not exceed the size limit set by your email provider.
5. If you have multiple attachments, try sending them with a file transfer service.
6. If you have an older email account, you may need to upgrade your service.