My Inmate Sent Me a Love Letter Meant for Someone Else

You probably already know the answer. The mail room did not do this. Incoming and outgoing mail at correctional facilities is handled by corrections staff, and while mistakes happen occasionally, deliberately switching the contents of two outgoing envelopes is not something that occurs on their end. This was his doing.

The more important question is what it tells you. A man corresponding romantically with another woman from inside is making a deliberate choice. Writing letters takes time and intent. He had to sit down, write that letter, address it, and hand it over. The fact that you received it instead of her is not the issue. The issue is that it existed at all.

He may have decided to come clean, and maybe that counts for something in your mind. But it is worth asking whether this is the first time or just the first time you found out. Loyal people tend to stay loyal regardless of their circumstances. People who stray tend to find a way to do that too.

What you do with this is entirely your decision. No one outside the relationship can tell you what it should mean to you. But do not spend time looking for an explanation that lets the mail room take the blame.