mxtoolbox "may be an open relay"

Hi there,

i searched all the Topics and found multiple Questions but no answer.

I configured some Mailprotection today after we got massive spam. (SPF,DKIM, dmarc). RDNS, Hostname etc is ok.

The only left over warning is this one:

SMTP Server Disconnected: May be an open relay.

With that SMTP-Message:

Connecting to ************

220 ************ ESMTP ready. [797 ms]
EHLO PWS3.mxtoolbox.com
250-**************** Hello pws3.mxtoolbox.com [64.20.227.134]
250-SIZE 104857600
250-8BITMIME
250-PIPELINING
250-AUTH PLAIN LOGIN
250-STARTTLS
250 HELP [828 ms]
MAIL FROM:<supertool@mxtoolbox.com>
250 OK [828 ms]
RCPT TO:<test@example.com>

SendSMTPCommand: You hung up on us after we connected. Please whitelist us. (connection lost)

PWS3v2 6297ms

The Smtp-log by the UTM:

2016:02:01-18:05:38 remote exim-in[29901]: 2016-02-01 18:05:38 SMTP connection from [64.20.227.134]:60937 (TCP/IP connection count = 1)