You have to run update.php when updating from 2.1 (even if there seem to be no updates) or clear caches by other means to regain access to the module settings page.
Unless Libraries API has a stable release, the 3.x branch of PHPMailer module will not become the recommended release. Module version 6.x-2.2 is otherwise feature identical to 6.x-3.0 and the 2.x branch will still be maintained in the future.
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.
#375422 by recidive: Fixed mails are sent to multiple recipients.
by sun: Added HTML mail preview when Mime Mail module is installed.
by sun: Simplified settings form (UX).
by smk-ka: Fixed improper RFC 822 formatted date (by Mime Mail).
by smk-ka: Fixed empty mail body with Mime Mail.
by smk-ka: Fixed inconsistent linefeeds with Mime Mail.
by smk-ka: Fixed phpmailer_debug_mail not always rerouting.