Cross posting is the act of posting the same information to multiple mailing lists. It also refers to the practice of posting articles to multiple Usenet newsgroups at the same time.

Excessive cross posting is considered bad form, because it multiplies the traffic on the Internet several times without adding any new content. In the extreme case, if all messages were cross posted to every group, then every group would look exactly the same. A cross poster can minimize this problem by specifying that all responses be directed to a single group.

Cross posting can be helpful if the message is of interest to a larger audience. However, cross posting to groups that are irrelevant to the message posted could be considered spamming.