using mautic 2.13.1 with php 5.6.36 or 7.0.30, I can not send any emails out of mautic.
I had tested it with the ´Test Mail´ function in EMail-Settings and send an email to a test contact using immediatly sending and queing.
In Email-Settings connecting to smtp and sending a test mail is signed as successfull, but no mails received the mailboxes. Mails sending outside mautic works even as receiving to the specific mail account.
Cron Jobs are set and working.
There is a fault in the System Info -> Logfile:
[2018-05-17 17:31:14] mautic.WARNING: PHP Warning - stream_socket_enable_crypto(): Peer certificate CN=
*.hosting.de’ did not match expected CN=smtp.domain.de’ - in file /var/www/vhosts/web456.dehamd121.servertools24.de/service.techfair.de/mautic/vendor/swiftmailer/swiftmailer/lib/classes/Swift/Transport/StreamBuffer.php - at line 94  
Later changed the name of the smtp server or disabled queing. But the warning still appears.
Thank you for your supporting response.