Claudio - This is a good question because some people make the mistake of processing and re-processing the entire folder of incoming e-mails on every refresh, rather than just the new incoming e-mails. Obviously, this slows import/refresh performance over time.
One option would be the ability to move each incoming e-mail to a separate specified IMAP/POP3 mail server sub-folder called something like "Read" once it is processed...this would preserve the e-mails in case someone else needed to consult them in future...would this help?
Moving every single email to a different folder once it is processed would solve the problem for us. We would be able to know it the email has been processed or not and will allow us to manually reprocess the email in case of need.
Are you going to make this feature available in the near future?