It is Kerio in the sense that the system is Kerio and what happens to the email is Kerio. The storing of the email in sent items (or somewhere) is important - the user needs to send the email again to make sure it went. Sometimes they have typed for 10-15 minutes and then lost it ??

Where did the email go is the real issue here ??

If I remember correctly there was a conflicts folder that would take messages when there was an issue. This gave you the opportunity to retrieve it after dealing with the issue, and send it.

If I recall correctly, Exchange does not let you send an email if you are over your quota (if set to do so). So it checked prior to sending the email. And it has options for receiving email despite the quota. Something I think is needed. We do not want to get client emails sent back. But to keep the user in check with restrict the sending until they delete emails.