TYPO3 Core

You try to send an email or your code triggers it somehow. But you use a not existing email address (localhost). You should make sure that you specify a correct TO and a correct FROM (!) address.

Yes, I use a version of TYPO3 4.5.2 and get the same error.

I am getting the same error when running the direct mail cron from the command line. The mailing is send and than the error is thrown. I guess this is because it is trying sending a confirmation that the mailing has begun, I am not receiving that email. The lockfile is not removed so the mailing is stalled until manual intervention.

PHP Fatal error: Uncaught exception 'Swift_RfcComplianceException' with message 'Address in mailbox given [@localhost] does not comply with RFC 2822, 3.6.2.' in /home/***/typo3_src-4.5.3/typo3/contrib/swiftmailer/classes/Swift/Mime/Headers/MailboxHeader.php:309
Stack trace:
#0 /home/***/typo3_src-4.5.3/typo3/contrib/swiftmailer/classes/Swift/Mime/Headers/MailboxHeader.php(239): Swift_Mime_Headers_MailboxHeader->_assertValidAddress('@localhost')
#1 /home/***/typo3_src-4.5.3/typo3/contrib/swiftmailer/classes/Swift/Mime/Headers/MailboxHeader.php(97): Swift_Mime_Headers_MailboxHeader->normalizeMailboxes(Array)
#2 /home/***/typo3_src-4.5.3/typo3/contrib/swiftmailer/classes/Swift/Mime/Headers/MailboxHeader.php(61): Swift_Mime_Headers_MailboxHeader->setNameAddresses(Array)
#3 /home/***/typo3_src-4.5.3/typo3/contrib/swiftmailer/classes/Swift/Mime/SimpleHeaderFactory.php(64): Swift_Mime_Headers_MailboxHeader->setFieldBodyModel(Array)
#4 /home/***/typo3_src-4.5.3/typo3/contrib in /home/***/typo3_src-4.5.3/typo3/contrib/swiftmailer/classes/Swift/Mime/Headers/MailboxHeader.php on line 309

I'm considering $TYPO3_CONF_VARS['MAIL']['substituteOldMailAPI'] = 0 (EDIT: solved the issue for now)

Could you look up, how direct_mail calls the mail API? Maybe it does sth. wrong (or the new SwiftMailer API has a limitation).

I found out that setting the replyto email and name in the Direct Mail > Configuration module solves the issue.

$headers[] = 'Reply-To: '.$this->replyto_email;

If it is not set it passes an empty header:

t3lib_div::plainMailEncoded($email,$subject,$message,implode(chr(10),$headers));

replyto does not have a safe fall-back when leaving it empty.

EDIT: The code is in ext/direct_mail/res/scripts/class.dmailer.php starting line 672

I filed a new bug #27633