For assistance, call: Crookston:  (218) 281-8000 Duluth:  (218) 726-8847 Morris:  (320) 589-6391 Twin Cities:  (612) 301-4357

The descriptions below explain the various reasons why we will consider a remote site to NOT be "well behaved", and thus subject to email blocking. DNS - Reverse DNS Reverse DNS allows us to associate a host name with an IP address. A large portion of our unwanted email originates, or is relayed through, systems that are not properly defined in DNS. This classification will be applied to areas of the Internet where we can pre-empt future abuse by requiring the remote site to be properly defined in DNS prior to sending us email. Procedure to have your site unclassified Define your site properly in Domain Name Service (DNS). You must have properly defined PTR and A records for your mail server. The IP address must map to a valid host name using a DNS PTR record. That host name must map to the connecting IP address using a DNS A record. In cases where there are multiple PTR records, ALL returned host names must map back to the connecting IP address. In cases where there are multiple A records, AT LEAST ONE returned IP address must match the connecting IP address. If you truly are unable to do this (e.g. your ISP does not allow it), contact us at mailadm@umn.edu for a possible exception. DSN - Delivery Status Notification A Delivery Status Notification (DSN), also known as a "bounce" message, is an email sent back to the original sender when a letter is found to be undeliverable. Most of the time, misaddressed email is rejected before it enters our systems. However, there are several conditions where our system accepts an email only to discover that it cannot be delivered. The system sending the original letter must accept a DSN for this error condition and remove the address from the mailing list. Example: Someone has elected to forward their email to another address. When we receive email for this individual, we accept the mail and then attempt to deliver it to the remote address. If this fails, we return a DSN to the original sender. Sites that do not accept DSNs have intentionally blocked all return communication. They continue to send email to undeliverable addresses. Procedure to have your site unclassified You must contact us at mailadm@umn.edu (never blocks mail). DUL - Dial-up Line or Dynamic IP Address Dynamic IP addresses are generally used by Internet connections which use a modem, DSL line, or cable modem, and are assigned by the ISP providing the service. These connections should never send email to us directly, but should either use the SMTP services of their ISP, or use our authenticated SMTP gateway (smtp.umn.edu). If your site was incorrectly classified as dynamic, you can request an exception. Contact us at mailadm@umn.edu (never blocks mail). INS - Insecure Server A mail system is considered insecure when it allows remote sites to send email through them to a third party. Such systems may be open relays, open proxies, virus-infected computers, or firewalls which are allowing other insecure servers through it. Many junk mailers use insecure systems in order to hide their identity and thwart efforts to block unwanted email. Procedure to have your site unclassified If your site is found on the list below, you will need to request to have it removed. Spamhaus Exploits Block List If your site does not appear on this list, you can request an exception. Send email to us at mailadm@umn.edu (never blocks mail). LOC - Local Mail Only If the recipient has selected "Allow email from local (umn.edu) servers only" as their incoming mail setting, then any messages blocked because they originate from a non-local mail server will have this code as the reason. OPT - Opt-in/out Sites that have failed to unsubscribe people from mailing lists upon request or have added people to mailing lists without permission have violated proper Opt In/Out procedures. These sites will be classifed as such. A new site that sends email to a large number of dormant accounts over a short period will also merit this classification. A dormant account is one which has not been accessed by the owner for a significant amount of time. It is not reasonable to assert that the people owning these accounts have subscribed to a mailing list with an email address they no longer use. Procedure to have your site unclassified You must contact us at mailadm@umn.edu (never blocks mail). OBL - Originator Address Blocked This reason is not associated with a remote server, but instead applies to the return address supplied during the SMTP session. A letter is blocked for this reason if the return address points to a domain which we have administratively blocked. Procedure to have your site unclassified You must contact us at mailadm@umn.edu (never blocks mail). PRV - Protocol Violation One or more elements of the SMTP transaction was in violation of the protocol or was otherwise deemed unsatisfactory. This is most often an indication of a virus. However, it may also be a misconfigured mail server, one which identifies itself (via SMTP HELO/EHLO) with a non-fully-qualified domain name or one which consists of one or more invalid characters. Be aware that the originator address of such email is most often forged. Procedure to have your site unclassified If a legitmate mail server is blocked for this reason, it is most likely that it is using an SMTP HELO/HELO value which does not conform to the RFC2821 standard. Its configuration should be updated to include a fully-qualified domain name. For further assistance, you may contact us at mailadm@umn.edu (never blocks mail). SPM - Known Source of Junk Mail Sites with this classification may appear on the list below. Spamhaus Block List If your site does not appear on this list, you can request an exception. Send email to us at mailadm@umn.edu (never blocks mail). UAA - Unauthorized Access Attempt Sites with this classification may appear on the list below. Spamhaus Policy Block List Sites may also have this classification due to having done one or more of the following: Attempted to use our servers as mail relays to a third party. Attempted to connect to the wrong server or service to transfer mail. Non-compliance with SMTP standards during mail transfer. Forging the address used on the SMTP "MAIL FROM" command. Procedure to have your site unclassified You must contact us at mailadm@umn.edu (never blocks mail). USR - User Block The recipient has specifically blocked your email address or domain. VIR - Virus Detected A virus or phishing message was detected during the content scanning stage and the message was discarded. Be aware that the originator address of such email is most often forged. Copyright 2002-2013 Regents of the University of Minnesota The University of Minnesota is an equal opportunity educator and employer. Last modified: Wed Sep 25 13:57:00 CDT 2013