What is the easiest and most convenient email ticket system?

Question

Helpdesk

The task is to process letters to technical support. Only work with email.
1. We accept email via IMAP or POP3
2. If this is not a response to an existing ticket, we assign the ticket number
3. We make a response to the letter with a quote and the ticket number in the subject line. With the ability to add your own headers, at least - the BCC field
4. Create a letter with the ticket number in the subject in the inbound for further response to it
5. It is desirable to be able to fasten your scripts for processing - subject, headers and body of the letter
Should work under debian. Perhaps just a library for php, python
No interfaces are needed - employees respond in any email client.
Free, not buggy, time-tested, working correctly with all encodings.

Answer 1

GLPI is not suitable?