Retrieve invoices

Hello is there a possibility to retrieve deleted invoice? and there a way to see sent emails to clients?

Actual accounting should not allow you to 'delete' an invoice. Have you tried your sent box with your email provider? (If you are using SMTP)

If you are using php mail(), if logging is enabled, check /var/log/mail.log

Invoice can be marked as 'closed' or 'void' but never should let you delete (afaik MYOB, Xero, ODOO all do not allow deletes)