Since 14 Jan I'm not receiving Alerts It seems to be a problem of the mail server.
I did the following test, and not receive it.
root@Observium:/opt/observium# ./test_mail.php -h rcn-rou-01
Observium 0.15.1.6218
Test E-mail Configuration
E-mails ENABLED globally ($config['email']['enable'])
E-mails use PHP-builtin MAIL backend ($config['email']['backend'])
E-mails use these default recipient(s) ($config['email']['default']):
E-mails send from ($config['email']['from']):
E-mails send to recipients based on default recipient from config and/or device sysContact.
Try send test notification for rcn-rou-01 to these email(s):
Notification for rcn-rou-01 SENT.