You are working with a partner from which you plan to fetch emails and you want to know if there will be any interference with their backup solution that reads emails via IMAP. As a result, you want to know what POP3 Delivery system Kerio Connect server users and what POP3 Delivery checks to determine which emails it should fetch.
The internal library being used for POP3 implementation is POCO POP3. You may review it as it is the library that negotiates the low-level functioning of the connection.
Unfortunately, we are unable to share more detailed technical specifications of the POP3 delivery service. However, the service is highly configurable and can serve your purpose to avoid interfering with the IMAP-based backup service.
You can read the article Configuring POP3 for Remote Emails and Applying Sorting Rules in Kerio Connect for the complete details.
Based on the need at hand to avoid interfering with an IMAP-based backup service, the following settings (inside Configuration > Delivery) might be of interest:
- Leave a copy of messages on the server.
- This setting is available in 'POP3 Download > Edit POP3 Account > Advanced > Retention Policy section'.
- By default, when you retrieve new messages from a POP3 email account, the messages are deleted from the POP3 mail server and then saved on the computer that you are using.
- This setting can help you avoid this so that the IMAP service can continue to back emails up without losing any emails.
- Per session download limits.
- This section is available in 'POP3 Download > Edit POP3 Account > Advanced'.
- If you believe that the POP3 download can generate load on the partner's server, you can use these settings to perform actions in smaller batches.
- Scheduled actions.
- This set of customizations is available in 'POP3 Download > Scheduling'.
- If you're concerned that the POP3 download will happen at the same time as IMAP and cause issues, you can schedule the POP3 downloads to happen at a time frame that's well outside the backup schedule.
Regarding the question of how POP3 Delivery determines which email it should fetch, the client and server cooperate on deciding which emails have been seen/downloaded already. When Kerio Connect asks the server for any new messages, the server may list messages already given to KC and so they will not be downloaded again. Once the emails are downloaded in Kerio Connect, everything else happens completely on the Kerio Connect side, not on the server.