"Mickey's Mix-Up" is a Mickey Mouse Works short starring Mickey Mouse. Originally aired during the show's third season, it was later featured in the House of Mouse episode "The Mouse Who Came to Dinner".
Mickey has just bought himself a new fax machine when he suddenly runs into Mortimer. After Mortimer insults him, Mickey arrives home and sets up his new fax machine, which he then uses to send a nasty letter to Mortimer. He then writes a love letter for Minnie and sends it through his fax machine.
Sometime later, Mortimer shows up on Mickey's front door, acting a lot friendlier to him than normal. When Mickey is confused as to why, Mortimer shows him the letter he sent and Mickey sees that it's his love letter that he meant for Minnie. Thinking he accidentally sent the nasty note to her, Mickey calls her to apologize, but she's actually not home right now. He dashes off to Minnie's house to take back the letter, but is too late, as he sees her taking a message out of her fax machine and then put it in her purse. Mortimer drives by and offers to take Mickey for a drive, but Mickey turns him down, saying he didn't mean to send the message that Mortimer got. Upset at Mickey breaking off their unintended friendship, Mortimer throws him out.
Mickey follows Minnie to the hairstylist's and, while she's getting her hair done, snatches her purse. Before he can remove the message, though, he runs into Pete, and the two get into a scuffle. Minnie then shows up with Chief O'Hara and has him arrest Pete, because they think he stole Minnie's purse and that Mickey was retrieving it for her. Minnie then looks at the fax she received earlier - which, it turns out, was actually a warning from Daisy about purse snatchers. Realizing he never actually sent that nasty letter to his girlfriend after all, Mickey now wonders who he did accidentally fax it to... and then the short ends on Roy Disney Jr. receiving Mickey's nasty note and asking, "Huh? What'd I do to him?"