Work issue, specific text in emails to external addresses returning 571 error

[bledd]

Bit of a strange one.

I'd rather not give the specific domain name in question.

I'll type an example though.



When we send emails externally, some staff have a specific line of text in their email signature.

Anyone with this text is suddenly getting 571 Delivery not authorised, message refused responses.

The text is..
http://www.ourdomain.com

If we send it like this..
http://ourdomain.com then it gets through no problem.

Anyone got any tips on where I can search online to whitelist this text?

To change multiple signatures for hundreds of users would be a real headache. Also replies to only emails wouldn't be working either.

Getting these responses from Gmail and Live.co.uk servers, not tried any others at the moment.

 

[bledd]

Requested #571 Delivery not authorized, message refused ##
From: example.
To: "example
Subject: FW: test17
Thread-Topic: test17
Thread-Index: AdJAylr0lzNHBDXITw2bBt3Jz5qUMAAAFzSw
Date: Thu, 17 Nov 2016 12:04:27 +0000
Message-ID: <example>
Accept-Language: en-GB, en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-originating-ip: [IP]
Content-Type: multipart/alternative;
boundary="_example"
MIME-Version: 1.0


Nothing useful :/

 

[bledd]

Overzealous spam filter update