Infrastructure
What is POP3 (Post Office Protocol version 3)?
An older protocol that downloads email to a single client and usually removes it from the server.
POP3 retrieves messages from a mail server to one device and, by default, deletes them server-side after download, providing no cross-device synchronization of folders or read state. It commonly runs over port 995 with implicit TLS, or port 110 with STARTTLS. It has largely been superseded by IMAP for modern multi-device and automation workflows.
Why it matters for cold email
POP3 is a poor fit for cold-email automation because it pulls mail to one place and can delete it, breaking the server-side mailbox that reply detection and inbox sync depend on. Deliverability platforms almost always require IMAP instead so replies, auto-replies, and bounces stay visible to the system.
Related terms
Stop guessing at deliverability.
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