Bad proofreading or clever ploy?

[P. Martin]

I knew as soon as I opened my mailbox today, what this letter was. 

I also immediately noticed a glaring error...

So, what do you think? Was this a sloppy mistake? Or a subversive marketing twist in order to get people to open the letter? Hmmmmm

[Darrie W. Bennett]

I think mistake.  Reason ... because if it was intentional, the sender would be taking a big risk, because the first thing I would think to myself is, " If this person missed this, he/she is probably not detail-oriented enough for me to want to work with".