When sending a private message to another member, if the original member does not already have a private conversation with that member, the subject will default to the title of the post. This will remain the subject until it is changed by going to the Conversations area within Mobilize.
At the top of the page, click the down arrow ("v" icon).
Choose Edit email subject line from the available options.
Click in the box, change the email subject line, and click the Update button.