This error drove me nuts! I contacted the hosts, deactivated plugins etc etc What finally worked was changing a line in /wp-includes/pluggable.php // $phpmailer->setFrom( $from_email, $from_name ); $phpmailer->setFrom( "wordpress@sistasinsuccess.info", $from_name, false ); I also created this email wordpress@[mywebsite.com] - so it … [Read more...] about Emails fail on multisite setup