The 3.x branch of PHPMailer module now relies on Libraries API, otherwise it is feature identical to 6.x-2.2 (which will still be maintained in the future). However, the 3.x branch will not become the recommended release until Libraries API has a stable release.
#642138 by Zoltok, sun, smk-ka: Fixed wrong path to class.smtp.php.
#563112 by markus_petrux: Added support for Libraries API.
by smk-ka: Improved error handling.
by smk-ka: Fixed PHP warning on Mime Mail settings page.
by smk-ka: Improved usability: provide next steps during installation.
#634868 by smk-ka: Fixed bad e-mail addresses in sent mails if display names contains a comma.
#491658 by a_c_m, smk-ka: Setting FromName also for Mime Mail messages.
#499824, #551004 by smk-ka: Added support for PHPMailer's exception handling to avoid dumping errors to the browser (since 5.0.0).
#516450 by smk-ka: Fixed test mail cannot be sent at the same time as enabling PHPMailer.
by smk-ka: Cleaned up Mime Mail integration. Ported the HTML e-mail preview to D6.
by smk-ka: Disabling the module now resets the smtp_library and mimemail_engine variables, to avoid a WSOD.
by smk-ka: Checking requirements before allowing to install the module.
by smk-ka: Documentation updates.
by smk-ka: Fixed PHPMailer settings not saved when used as Mime Mail engine.
by smk-ka: Fixed Admin Menu not visible anymore.
by smk-ka: Regression: Fixed not being able to enable either Mime Mail or PHPMailer for e-mail delivery.
by smk-ka: Moved resetting email properties to DrupalPHPMailer::SmtpSend().
by smk-ka: Provide more user-friendly error messages.
#607204 by smk-ka: Added support for Reply-To headers.
#633278 by smk-ka: Increased security: added an option to hide the password on the settings page and added a log message if the configuration changed.
#686994 by sun, smk-ka: Restored compatibility with PHPMailer 2.x library.
#675388 by smk-ka: Fixed unrecognized character in regular expression for PHP versions < 5.2.2.
#607204 by dagmar, smk-ka: Fixed unable to reply to e-mails sent via Google Mail. Added an option to always set a "Reply-To" address.
#764448 by smk-ka: Fixed sending more than one message for certain server configurations.
by smk-ka: Fixed libraries module not loaded when checking install requirements.
#847238 by J0nathan: Better description of debug settings in README.txt.
#805834 by smk-ka: Added description of the most common error message to README.txt.