What are collectors?
A collector is a configuration where you tell the archive system how to retrieve/accept data from your email server/site. Depending upon the type of email platform you are using, you may choose to process your email into the archive service using a PUSH model (SMTP) or a PULL model (POP).
When SMTP collector is enabled on your ACCOUNT tab. A Configure SMTP Collectors option will be revealed on your COLLECTORS tab. Here you will be provided with a unique address to forward archived emails to the service for processing. You can also lock down the origination point of these emails by adding your servers external IP address(es) to the Trusted Network range
In the PULL scenario using POP you may need to make some modifications to your email server or firewall. Most organizations already have POP/IMAP enabled, so all you need to do is make sure the POP port is accessible to the Internet.
You can create a simple secure firewall rule to only allow inbound SSL POP connections from the archive system's data centers. See the firewall configuration notes for more details.
The following video will give you an overview of how you implement a collector.
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You may also be interested in how to create a Groupwise collector.