Here, I’ll make you feel better.
When I was first trying to get freelance copyediting work, I did a mailing of about 40 cover letters and resumes to targeted potential clients. I made up a form letter with merge fields, which I merged with my (I thought) carefully vetted data file of names and addresses to create the mailing.
After they had been sent, I found that in one of the letters I had spelled the receipient’s name differently in the address block and in the salutation! Worse, it was the dreaded ie/ei transposition, which I am forever correcting other people for making IN MY OWN NAME!!
I was mortified. Needless to say, I never heard from that person.
Here’s another one. Mr. S almost, ALMOST sent a cover letter with a job application telling the recipient how much he enjoyed sampling microbrew beers. The intended recipient was a machine shop. The PREVIOUS recipient, whose stored letter on his computer he had used as a template, was (you guessed it) a microbrewery.
Luckily he caught it before he sent it out (although he didn’t get either job). But we laughed at what the machine shop supervisor’s reaction might have been.