phpBB.com

How do I see private messages sent by users in my forum?

You can't in vanilla phpBB, the clue is in the name "private". I personally wouldn't use a board that spied on my pm's but there have been similar requests in the past, you will need an extension for that.

There are extensions for it, yes.
But: depending on the laws of the country in which you live, you make yourself liable to prosecution if you read the personal messages of your users.

Not a good idea, I said my 2 cents in the past about this in this topic viewtopic.php?f=556&t=2503491

So just going to copy and paste that reply.

"Not to sound negative about this but is it nice to read private communications between others, I think not. Never mind that it could also be a privacy violation and potentially be legally hot water. I have never done it on my forum in 14 plus years and would not recommend anyone else to do it.

All the best.

Peace"