Software Development:
Individual Programming

Symptom

You have sent an e-mail, but the recipient refuses to receive the e-mail with a note similar to this:

mail. [] said: 554 5.7.1 Service unavailable; Client host [] blocked using dnsbl.sorbs.net; Currently Sending Spam See: http://www.sorbs.net/lookup.shtml? (in reply to RCPT TO command)

Cause

The IP address of your Bitpalace mail server is an alleged spammer on the SORBS DNSBL (www.sorbs.net) blackhole list. Recipients who follow the instructions block mail reception. The malformed SORBS list blocks many mail servers for no reason. Occasionally Bitpalace hosts.

Because you, as a victim, may think we are biased:

"SORBS is occasionally under criticism, as well-known e-mail providers are repeatedly listed, which in the past included Gmail, Hotmail, web.de, Strato, freenet.de, GMX and T-Online In practice, uncritical use of the SORBS DNSBL blocks legitimate e-mails from numerous users. "

Translated from source: http://de.wikipedia.org/wiki/SORBS

“Due to some questionable and aggressive techniques, SORBS regularly creates false blacklist entries for legitimate mail servers.”

Source: https://en.wikipedia.org/wiki/Spam_and_Open_Relay_Blocking_System

SORBS has been criticizing misconduct for years:

https://www.heise.de/ix/meldung/GFI-will-SORBS-auf-die-Spruenge-helfen-1152258.html

Even large providers like Google complain that their servers are blocked by SORBS:

“After investigating further, I have confirmed that there is a range of Google IP addresses that SORBS has blacklisted and has not yet agreed to remove, despite our attempts at negotiating with them to do so. To move forward, I recommend that you contact the recipient and request them not to block Gmail IP addresses based upon SORBS.”

Sources: https://productforums.google.com/forum/#!msg/apps/kAKXX1fCYf4/dURMAMyGAQAJ, https://productforums.google.com/forum/#!msg/apps/WjzMWHorSSs/kuUjoxqyEOYJ

SORBS has occasionally listed hosts from us in the past because we have rejected spam to the sender, i.e. our customers were protected against incoming spam. These rejected mails were received by SORBS and deemed to be spam supposedly sent by our host.

We have also been listed by SORBS before, because the autoresponder of a customer has informed the sender that the customer no longer uses the e-mail address provided.

Although in both cases we have proved to SORBS support by means of log files that SORBS lists the mail server IP unauthorized, some IPs are not arbitrarily released there.

Solution

Bitpalace works closely with many procedures to ensure that our hosts do not send spam. Outgoing spam is detected and blocked very quickly here. Customers are informed by us and cannot send any further emails until the problem is resolved. Entries from our hosts in SORBS have always been false or grossly negligent.

Please contact the recipient who rejects your e-mail due to a SORBS DNSBL entry and suggest there - with reference to Wikipedia, the Heise coverage, the Google quote, or simply with reference to this article - to renounce the use of the SORBS DNSBL. Recipient servers that use the SORBS list can generally not receive e-mails from any of the major German Internet access providers because their mail servers are also blocked there. The use of SORBS is therefore a bad decision anyway. It is in the interest of server operators not to use SORBS as DNSBL.

Mail administrators can use many other well-working, well-functioning blackhole lists and do not need to rely on the malformed SORBS list, for example, sbl.spamhaus.org, xbl.spamhaus.org, bl.spamcop.net, and b.barracudacentral.org.

Overview of frequently asked questions