Money laundering and SAR.

[Fedup]

Unless you use a special pen then checks that fall into the wrong hands such as being picked out of the mail can be "washed" where the ink is removed from the check leaving only the signature.

https://en.m.wikipedia.org/wiki/Check_washing

I never put any check in the mail box, always drop them at the blue post office box. So that reduces the problem. I started doing this after I was told by a friend who saw her outgoing mail being stolen by thiefs.
For mobile checks, I keep the checks here at home, after depositing.

 

[copyright1997reloaded]

There is a limit of $100k ACH transfer per day. I've done this on multi banks, for overseas it's GBP 100k per day.

This is a bank imposed limit, not a limit on ACH. I just recently did a single ACH over 100k.

 

[meierlde]

I never put any check in the mail box, always drop them at the blue post office box. So that reduces the problem. I started doing this after I was told by a friend who saw her outgoing mail being stolen by thiefs.
For mobile checks, I keep the checks here at home, after depositing.

Note that if you have just a mailbox on the outside of your house or a curbside mailbox it is likley as there is no lock. The mail slot on a cluster box is a locked door with a letter sized slot so it would be harder to steal the mail. (another advantage of the cluster mail box beyond the locked individual box)