Email handler using IMAP deletes emails from inbox

Problem Definition

According to the documentation emails retrieved by the email handler are not deleted from the mailbox:
https://confluence.atlassian.com/adminjiraserver076/creating-issues-and-comments-from-email-945111600.html#Creatingissuesandcommentsfromemail-POPorIMAPemailmessages

On an IMAP mail server processed messages are not deleted but marked as read.

But when an email is handler is created using IMAP the emails are deleted.

Steps to reproduce:

1. setup a mail server connection with IMAP protocol
2. create an email handler using this connection
3. Send and email to the account.

Expected Result:

Processed emails marked as read.

Actual Result:

Processed email are deleted from inbox.

Note on fix

The current ticket is not a bug, but more like a feature request for new functionality for IMAP handler. In short, we are introducing a new UI control "mark as seen" checkbox for Mail handlers using IMAP.
See JRASERVER-62660 for more details.