PHP imap_headerinfo() Function: Usage and Examples

Returns structured header information for a single message. This guide demonstrates its use in PHP code and explains when the result or side effect needs extra checks.

What It Does

Returns structured header information for a single message.

Syntax and Parameters

The examples below show a real call to imap_headerinfo with suitable arguments. Read the function call in context: its connection, handle, input data or other prerequisites are created before use.

Requirements: IMAP PECL extension in PHP 8.4+; a TLS-protected mailbox.

Compatibility and security: As of PHP 8.4 the IMAP extension is installed separately from PECL.

These examples are for an isolated development environment. Hostnames, credentials and remote paths must be replaced with your approved configuration.

Example 1: Core Behavior

Read-only mailbox example where the API supports it.

<?php
$user = getenv('IMAP_USER'); $pass = getenv('IMAP_PASSWORD');
$server = getenv('IMAP_HOST');
if (!$user || !$pass || !$server) throw new RuntimeException('Missing IMAP settings');
$mailbox = '{' . $server . ':993/imap/ssl}INBOX';
$mb = imap_open($mailbox, $user, $pass, OP_READONLY);
if (!$mb) throw new RuntimeException("Mailbox unavailable");
$value = imap_headerinfo($mb, 1);
echo $value === false ? "Unavailable" : json_encode($value, JSON_PARTIAL_OUTPUT_ON_ERROR);
imap_close($mb);

Observe the returned value or changed resource state. A successful function call can still require additional checks before a higher-level operation is considered successful.

Example 2: Alternative or Failure Case

Check the outcome against the active mailbox and its message sequence numbers.

<?php
$user = getenv('IMAP_USER'); $pass = getenv('IMAP_PASSWORD');
$server = getenv('IMAP_HOST');
if (!$user || !$pass || !$server) throw new RuntimeException('Missing IMAP settings');
$mailbox = '{' . $server . ':993/imap/ssl}Support';
$mb = imap_open($mailbox, $user, $pass, OP_READONLY);
if (!$mb) throw new RuntimeException("Mailbox unavailable");
$value = imap_headerinfo($mb, 1);
echo $value === false ? "Unavailable" : json_encode($value, JSON_PARTIAL_OUTPUT_ON_ERROR);
imap_close($mb);

Compare the different inputs, environment assumptions or result checks. Do not use a transport-level success value as proof that all business-level requirements were met.

Practical Example: Applying the Rule

For live mailboxes use stable message UIDs and review any destructive action first.

<?php
$user = getenv('IMAP_USER'); $pass = getenv('IMAP_PASSWORD');
$server = getenv('IMAP_HOST');
if (!$user || !$pass || !$server) throw new RuntimeException('Missing IMAP settings');
$mailbox = '{' . $server . ':993/imap/ssl}Archive';
$mb = imap_open($mailbox, $user, $pass, OP_READONLY);
if (!$mb) throw new RuntimeException("Mailbox unavailable");
$value = imap_headerinfo($mb, 1);
echo $value === false ? "Unavailable" : json_encode($value, JSON_PARTIAL_OUTPUT_ON_ERROR);
imap_close($mb);

In an application, convert low-level failures into controlled responses and log only non-sensitive diagnostic context.

Important Behavior and Edge Cases

Raw sender fields are untrusted input; escape before placing them in HTML.

IMAP message sequence numbers can change as mailbox contents change; use UID-based options when stable identifiers matter.

Comparison with Related Functions or Patterns

Common Beginner Mistakes

Key Takeaways

• Returns structured header information for a single message.
• Raw sender fields are untrusted input; escape before placing them in HTML.
• imap_fetch_overview reads a compact summary for multiple messages.

Select this API or pattern based on its documented behavior and the trust boundaries in your own application, and test all external integrations against their actual deployments.