This page explains the reasons for email rejections and provides you with a channel to communicate with the
email server administrators.
The email server to which this page refers is tango.tkos.co.il. This server provides email services and spam
filtering services for the following domains:
If you reached this page it is probably because we rejected your email to some address at one of the
We reject emails for the following reasons:
- The domain portion of your From address is a domain that does not exist. This should not happen to legitimate senders unless
you mis-typed your email address when configuring your email program or the registration of your domain name expired. In this case you
will see a message like:
553 5.1.8 ... Domain of sender address email@example.com does not exist
- Your email was relayed to us by a server with no DNS name. In this case the reject message that you received would look like this:
550 5.7.1 Rejected IP with no reverse lookup. See explanation at http://tk-open-systems.com/unblockme/index.php
- Your email was relayed to us by a server whose DNS name does not look like a legitimate email server. We block "pool addresses", that
is, email relays whos DNS names look like they are default names that ISP's give to ADSL lines, like
"adsl-134-21-192-81.adsl.iam.net.ma". In this case the message that you see looks like this:
550 5.7.1 Rejected pool address. See explanation at http://tk-open-systems.com/unblockme/index.php
Sometimes legitimate email comes from pool addresses when businesses set up their own email server but do not change the DNS lookup
of the IP address of their email server from the default address that their ISP assigned.
- Your email looks like a forged gmail, yahoo, hotmail address. Spammers often try to trick us into relaying email by forging the From
address so that it looks like it is comming from a gmail or yahoo account. We perform a check on email with From field that have
hotmail, yahoo, gmail and other commen webmail provider domain names to verify that the sending email relay belongs to the provider.
If not, then we block the email. Occaisionally people sending legitimate emails to our user through non-gmail or non-yahoo server use
their gmail or yahoo address in the From field of their email and of course we block it. If this happened to you, then please put your
yahoo/gmail account address in the Reply-To field instead of the From field of your email. The rejection message looks like:
550 5.7.1 Rejected forged sender domain from firstname.lastname@example.org [adsl-184.108.40.206.viola.net]. Details at http://tk-open-systems.com/unblockme/index.php
- Your email was sent through a server that we have explicitly blocked because we received spam from it in the past and it appears
to us that the administrators of the server are not policing it properly. In this case the rejection message will look like this:
550 5.0.0 ... http://tk-open-systems.com/unblockme/index.php
Please use this form to contact us with the details of the error message that you received.