Are you sending an email with attachments?
Many attachments will be blocked by default (exe files, password protected zip files) as they may contain malicious content, try sending the email without the attachment
Can you try sending the same email to a non-eyos address?
If this also fails, you may have an outbound mail filter and need to contact your internal infrastructure team to find out the reason for your mail being blocked.
You can always access https://support.eyos.one and submit the ticket through there.
tags: bouncing, support@retail.eyos.one, attachments