Opened but unmolested mail?

So a few months ago, I received a few checks in the mail for my birthday. When they got to me, the envelopes had been carefully slit open (apparently by machine) but nothing inside appeared to have been taken or otherwise disturbed. Anyone got an explanation? This was the case for three envelopes containing checks, but not for a couple others from other people.

What gives?

Are you saying that other envelopes had been opened and the contents taken

No, nothing had been taken from anything. The only weird thing is that three of the envelopes had been opened.

Did the sender happen to use those envelopes which have the stamps pre-printed on them, or neglect to put on a return address?

The reason why I ask is that the same thing happened to me back during the anthrax scare because I did both of those things. I mailed a check to my mother-in-law which was severely delayed in reaching her. When it arrived, it had been opened and re-sealed.

Nothing weird about it. As an ex postal worker I can tell you that sometimes mail gets caught in the MLS machines and this can open them neat as a pickle

While I had a UPS Store, we got several pieces like that. Customers always suspected us and we jud explained that it happened all the time and sent them to either the PO or the sender. It does happen a lot. No idea why, though.

The post office stamps the mail it opens for inspection, so you know it has been opened and resealed. They didn’t open it to inspect it.

I used to work at the PO.
Once opened by the PO, your letter will be put into a baggie with a slip that says why, “Opened for Postal Inspection”, “Damaged in transit” etc.
If it’s not in a bag, they didn’t notice the damage until it got to the carrier, who probably also didn’t notice.

Or, and this may shock you, there can be illegal activity at the post office.
It’s pretty easy for anybody to get a job there if they have no prior record. The “test” is whether you can distinguish 1177 from 11777 and Johnson from Johansen. Best score gets the Christmas rush temp night shift job.
Those people may be desperate and have friends who urge them to “accidentally” slit mail hoping for the types of checks that are worth forging and are easy to bleach and modify.
Not big news, but happens every year.

Maybe they opened it looking for cash, but finding only cheques left it alone?