Just some context - I work for clients as my job, and once I'm finished doing the work for a particular client, I give my clients' documentation to my colleague to send away in the post back to the client.

Issue is, I can't remember whether I sent documentation back for various clients given I finished their work a full month ago, so if ever I consciously think about it, I worry - did I ever actually do this, or have I lost the data? 

How do I stop thinking in this way?

(I'm not in the position to email the clients given I'm a junior employee)