Error: "550 5.7.1 Email rejected because IP address has been listed by an Internet spam block list"


After sending email to a recipient with a TechMail address (, you may receive an error message similar to the following:

550 550 5.7.1 Email rejected because the IP address X.X.X.X has been listed by an Internet spam block list [1].


The message you received indicates that the sending IP address X.X.X.X has been blacklisted by at least one Internet spam block list.


Wait until the block is automatically removed.

In an effort to reduce the amount of junk email received by TechMail accounts, Texas Tech University enlists a number of industry best practices. One such tactic is to use resources of public spam reporting services. These types of services employ many measures to determine the true source of spam and consolidate reports into blacklists which are provided to Internet service providers (ISPs).

When a blacklist occurs, the TTU IT Division blocks the servers which are blacklisted. A server is automatically removed from the blacklist by spam reporting services after a period of time to test whether spam continues to be reported. The process is automated and based on the behavior of the sender's email systems; it is not based on actions of TechMail customers or actions of TTU email administrators.

It is worth noting that the sending server may become blocked again if reports resurface of sending an inordinate amount of spam. This type of filtering technology is intelligent and makes changes on its own based on information obtained from constant analysis of incoming email messages. The time of the block may also vary due to the intelligent nature of this type of email feature.

TechMail's spam filtering has saved the TTU community from receiving millions of unwanted spam emails. It also serves to keep our TechMail system safer and cleaner. If you receive this non-delivery message again, wait a period of time and attempt to resend your message, as the block may have been lifted. You may also choose to contact the system administrators for the sender's mail system to alert them about this problem with their email system. In the meantime, you may use alternate email services or other means of communication.

TIP: To check if an IP address has been blacklisted, you can visit