Multiple plugins are sending each message twice. My other sites on same host don't have this p

One of my installs (I have several on the same web host) is sending emails twice. Seems like any plugin that is generating mail gets two copies sent to each recipient but the “New User Registration” and “Password Lost/Changed” emails don’t get double-sent.

Any idea what would cause emails generated by plugins to be duplicated.

The two I know are doing this for sure are:

EZPZ Backup

Subscribe2

I use BOTH of these on another blog and don’t have this problem. This is my only 3.2.1 version blog and my web host is probably running an earlier version of PHP5 than the latest.