IMAP — server-side mailboxes with folders, flags, and search, kept in sync across devices.
Clients issue tagged commands (CAPABILITY, LOGIN, SELECT, FETCH, SEARCH) and the server keeps the authoritative state, so messages, flags, and folders look the same on every device. Port 143 is the cleartext port; the STARTTLS upgrade happens here, while implicit TLS runs on 993, which is what most clients now use. Dovecot and Cyrus are the common self-hosted servers, and 143 is often left open for LAN clients and migration tools. IMAP is retrieval only — sending still goes out over submission on 587.
Expose with care
Expose only with STARTTLS required before LOGIN; plain 143 sends mailbox credentials in the clear, so prefer 993.
$ printf 'a1 CAPABILITY\r\na2 LOGOUT\r\n' | nc -v MAIL_HOST 143Seen this on your network? Beige Box scans your Wi-Fi and shows every open port on every device — and its Ports tool links straight back here.
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Corrections or a missing port? Reply @rimrocksystems.