Breaking: #88643 - Removed swiftmailer/swiftmailer dependency

See forge#88643

Description

TYPO3's dependency swiftmailer has been removed in favor of new symfony-based components "mime" and "mailer".

This means that all SwiftMailer-related PHP code has been removed.

Impact

Custom SwiftMailer plugins or transports cannot be used without further migration anymore and will result in a fatal E_ERROR.

Using SwiftMailer-specific API by using TYPO3's \TYPO3\CMS\Core\Mail\MailMessage class might result in fatal E_ERROR when sending out emails.

Affected Installations

Any TYPO3 installation with third-party extension sending out emails or extending TYPO3's email sending capabilities.

Migration

Search the third-party extensions' code for occurrences of MailMessage or parts starting with \Swift_ and migrate to symfony/mime or symfony/mailer APIs, which are included in TYPO3 v10.0.

If required, SwiftMailer code can be installed via composer (when running TYPO3 via composer) via composer require swiftmailer/swiftmailer.