Error: "550 5.1.1 User unknown" when emailing a TechMail functional mailbox or distribution list


After sending an email message to a TechMail ( distribution list or functional mailbox, the sender receives an error message similar to the following:

EXAMPLE 1: does not like recipient
Remote host said: 550 5.1.1 User unknown
Giving up on

example screenshot


Restriction in the System Prevented Delivery of the Message


Action: failed
Status: 5.1.1
Diagnostic-Code: smtp;550 5.1.1 User unknown


By default, TechMail distribution lists and functional mailboxes can only receive messages from senders inside the TechMail system. When requesting a new address, NSCs can specify whether they want to override the default setting and allow the address to receive email from the outside Internet.

Also, after a mailbox or distribution list is created with permissions to receive email from outside the TechMail system, or after its permissions are later changed, it will be up to an hour before outside senders can email that address.

Additionally, the owner of the distribution list or mailbox may have also requested other restrictions on who can email that address.


If the mailbox or distribution list was newly created, or if its permissions recently changed, please wait at least one hour. Then, try emailing the address again. This gives the permissions time to propagate through the TechMail system.

If the mailbox or distribution list has permissions restricted on purpose, try sending your message from an authorized address, such as a TechMail address. If desired, you may place a request to have the restriction(s) lifted by contacting the owner of the distribution list or functional mailbox. The owner can submit a functional mailbox assistance request if assistance is needed in modifying the restrictions on the functional address.

You can find the owner of a distribution list by going to the global address list (GAL) in Microsoft Outlook and viewing the properties of the distribution list. Some distribution lists may not have owners.

NOTE: There are special distribution lists such as "TTU - Staff", etc. that are reserved for special purposes. Communication through lists that go to a wide audience should come from executives and upper-management at Texas Tech (that is, Office of the Chancellor, Office of the President - TTU, Communications & Marketing, etc.). Wide communication from most email users to the Texas Tech community should be sent through channels established for such purposes, such as TechAnnounce.

Functional mailboxes may have multiple owners. The best procedure is to contact an NSC for the department/college/organization under which the mailbox falls.

If the owner of the distribution list or functional mailbox would like the address modified to receive non-TTU domain emails, an IT Help Central full-time staff member can make the request by assigning a service catalog task to TechMail administrators. IT Help Central staff will only place such a request after verifying with the owner of the address or an NSC that it is acceptable to make the change.


If the owner of the functional address chose to remove the restrictions, the sender will be able to send emails to the list successfully after one hour has passed. Otherwise, the address can be emailed from inside the TechMail system from another address.