I've got ispconfig3 now up and running well. I've got several mail accounts set up, but occasionally I need to get into the mails and read their content without using the proper login for the account. Is this possible through command line or otherwise?
You can go to the Maildir of a user - there are three directories, cur, new, and tmp. The mails are stored in these directories, one mail per file. You can open them with cat or vi, for example.