Mattermost allows users to export the posts from a single channel. 

Note:  This process also works for direct message conversations.

Navigate to the channel.

Type /export and press Enter/Return.

The export starts and a confirmation is displayed on the screen

The channelexportbot will send you a Direct Message once the export is ready.

Open the direct message.  The exported posts are provided in a csv file.

Click on the download symbol in the direct message, modify Save As and location (i.e. Where) as necessary, and click Save.

The format of the exported channel data is listed below:

|Post CreationTime|User Id|User Email|User Type|User Name|Post Id|Parent Post Id|Post Message|Post Type|