Email being blocked by exhchange

[Adam1V]

I have been having troubles with emails not getting through to another company.

Initially, I blamed them as its the first case ive heard.

As a work around, ive sent it to a friends personal email address (hotmail), which has flagged up the email as "This message has been blocked for your safety." and "This message may be a phishing scam. Learn more"

The only attachment is a small image (named 01.jpg) which is in the signature.

As ive said before, this doesnt happen anywhere else.

Would anyone know what could be causing this to be picked up as a potential phising scam?

*edit*

Something which I've just considered, we dont actually have any pop3 accounts for the addresses which are sending emails, we have a single collect all which is obviously sent via our ISP's smtp server.

Could this be affecting it?

I forgot to mention, the above emails are not arriving in the exchange server and being passed to the intended recieptant, they are simply not coming through.

They have SBS 2003 installed and plain old Exchange Server 2003.

[Kosh]

First you should check your sending (SMTP) Mailserver here: http://www.mxtoolbox.com/blacklists.aspx

It is hard to say what causes the error.

It could be a missing rDNS entry, wrong SenderID/openspf entries, a blacklisted Mailserver, ......

Without more information like sending domain, mailconfiguration, IP-Addresses, etc. I can only guess.

If your exchange server sends your e-mails via your company's NAT ip to the internet, then you could simply telnet into other company's mailserver and see what error you get if you try to send a mail this way.

[Adam1V]

I've just tested this again to hotmail, and it appears to be related to the sender ID.

When I click 'More Info' in Hotmail, it takes me to a page;

About Sender ID, spoofing, and phishing

Sender ID is a technical solution started by Microsoft and other industry leaders to help fight spoofing (Sending messages with fake or stolen account information.) and phishing (Falsely claiming to be a legitimate business to send you to a fake website or scam you into giving out private information.) , which are the two primary deceptive practices used by senders of junk e-mail (Unwanted, unsolicited, or illicit e-mail or other electronic messages, including spam.) . For more information, visit the Sender ID Framework Overview webpage.

Notes

Windows Live Hotmail treats all messages that fail Sender ID and phishing tests as fraudulent and warns the user about opening these messages. For information about how to read blocked e-mail messages, see Block or allow messages from specific senders and domains.

If you experience difficulties when you use another mail service to send your mail, but you use your Windows Live Hotmail address as the sending address, contact the network administrator of the other service for help.

This could possibly why their exchange is not allowing it through?

That aside, is there a way to get around the sender id problem?

[Kosh]

Yes.

Create a senderID TXT entry on your DNS or your ISP's DNS server (whoever hosts your MX record).

With this wizard you can easily create the correct entry:

http://www.microsoft.com/mscorp/safety/content/technologies/senderid/wizard/

[+BudMan MVC]

yeah if your having a 3rd party server sending your email for you, like a ISP smtp server - you would want to add the IPs of this/these servers to your SPF record for your domain.

Who is hosting your dns for the domain that your email comes from? Get with them on creating the SPF record, if they do not support it - you may want to move where your dns for that domain is hosted at.. Your prob going to run into this more an more as domains start bring better spam/phishing filtering online.

Here is a great place to get up to speed on what SPF is

http://www.openspf.org/

As to a way around it?? NO not really -- the receiving server checks the dns the domain the email says it comes from, if the IP of server they are getting the email from that says its from an address in say domainX.com, if the SPF record does not list that IP for domainX.com -- then its a possible spam/phish and sure they might block it or flag it. The only way to prevent that is to have SPF records for email servers that are authed to send email for your domain.