IMAP and PHP 8.4: why WordPress email plugins break, and what to do

What changed in PHP 8.4

php.net lists the extensions that left PHP with version 8.4, IMAP among them, which “have been moved to PECL and are no longer part of the PHP distribution” (php.net): IMAP, OCI8, PDO_OCI and PSpell. PECL is where PHP extensions that aren’t part of PHP itself are published; a host can still install them, but they no longer come with PHP.

What happens on the server

We ran the same check on the official PHP builds. The PHP 8.3 build still includes IMAP as an extension:

<?php
echo function_exists('imap_open') ? 'IMAP available' : 'IMAP missing', "\n";

IMAP available

The PHP 8.4 build doesn’t include it, so the function doesn’t exist, and a plugin that calls it stops:

<?php
echo function_exists('imap_open') ? 'IMAP available' : 'IMAP missing', "\n";
$inbox = imap_open('{mail.example.com:993/imap/ssl}INBOX', 'user', 'password');

IMAP missing

Fatal error: Uncaught Error: Call to undefined function imap_open() in /var/www/html/wp-content/plugins/mail-inbox/mail-inbox.php:3
Stack trace:
#0 {main}
  thrown in /var/www/html/wp-content/plugins/mail-inbox/mail-inbox.php on line 3

On a WordPress site that means “There has been a critical error on this website.” on every page that loads that code, and often the plugin’s background task (checking the mailbox) fails silently in WP-Cron.

Which plugins are affected

Plugins that read email: help-desk and ticket plugins, plugins that turn emails into posts or comments, bounce and reply handlers, some newsletter tools. Plugins that only send email are not affected: WordPress sends mail with its own functions, not IMAP.

Before you switch to PHP 8.4

Note what a code check can and can’t tell you here: the imap_* calls are ordinary code, and whether they work depends on what your server has installed, not on the PHP version alone. CompatNav doesn’t flag them for PHP 8.4. The decisive check is the extension on your server, and your host is the one to ask. The rest of the PHP 8.4 changes are in WordPress and PHP 8.4; other missing extensions show up in Site Health’s module check.