Hi:
same problem here. I've deactivated all plugins and this is the result of the Diagnostic Test:
OS: Linux apolo.fmserver.net 3.10.0-233.1.2.lve1.3.33.4.el7.x86_64 #1 SMP Thu Jul 30 08:48:17 EDT 2015 x86_64
HTTP User Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:41.0) Gecko/20100101 Firefox/41.0
PHP: Linux 5.6.14 C
PHP Dependencies: iconv=Yes, spl_autoload=Yes, openssl=Yes, sockets=Yes, allow_url_fopen=No, mcrypt=Yes
WordPress: 4.3.1 es_ES
WordPress Theme: Betheme Child
WordPress Plugins: Postman SMTP
WordPress wp_mail Owner: /home/sdwpodyn/public_html/prueba/wp-includes/pluggable.php
WordPress wp_mail Filter(s): wp_staticize_emoji_for_email
Postman: 1.6.24
Postman Prevent Message Sender Override (Email|Name): No | No
Postman Transport Status (Configured|Ready|Connected): No | No | n/a
Postman Deliveries (Success|Fail): 0 | 0