IMAP

How Telescope verifies IMAP server availability, greeting health, and TLS capability.

IMAP monitors verify that a mail server accepts IMAP connections and responds correctly to a protocol handshake. Checks do not authenticate and do not inspect mailbox content.

How a check works

Telescope opens a connection to the configured host and port.
It reads the IMAP greeting and validates server readiness (* OK or * PREAUTH).
Telescope sends CAPABILITY to collect advertised server features.
If TLS is required, Telescope negotiates TLS using either:
- STARTTLS (explicit TLS upgrade), or
- implicit TLS (IMAPS, commonly port 993).
Telescope re-runs CAPABILITY after STARTTLS, sends LOGOUT, and stores structured protocol details.

Status classification

Condition	Status	What it means
Handshake succeeds and policy checks pass	Up	IMAP endpoint is reachable and protocol flow is healthy
Connection timeout/refusal/DNS failure	Down	IMAP endpoint is unreachable
Malformed or unexpected protocol replies	Down	Server is reachable but not speaking expected IMAP flow
TLS required but secure transport unavailable	Down	Server does not satisfy monitor TLS policy
Greeting/banner verification fails	Down	Server identity/content check failed

IMAP monitors currently classify results as up/down (no degraded state).

Configuration options

Setting	Default	Description
`port`	`993`	IMAP endpoint port
`requireTls` / `requireStartTLS`	`false`	Require secure IMAP transport
`implicitTls`	auto (`true` on port `993`)	Use TLS immediately on connect (IMAPS)
`verifyBanner`	unset	Optional substring that must appear in server greeting

Result data highlights

IMAP checks store structured metadata in result_data, including:

connection_mode (plain, starttls, implicit_tls)
banner, greeting_status
supports_starttls
tls_active, starttls_negotiated
tls_protocol, tls_cipher
capabilities (advertised by CAPABILITY)
response_statuses (OK, NO, BAD, BYE, PREAUTH)

Operational notes

STARTTLS checks refresh capability state after TLS upgrade, as recommended by IMAP TLS guidance.
If you need certificate trust/expiry validation, pair IMAP monitors with an SSL monitor on the same host/port.