Is there such thing as “a written malapropism” or “a slip of the pen”? Or are they just simple spelling mistakes? If they were unintentional, they couldn’t be considered puns or a play with words, I presume.
The one you’ve listed (presuming the qoutes are yours) is a simple homophones:
(Linguistics) one of a group of words pronounced in the same way but differing in meaning or spelling or both, as for example bear and bare.
It’s not a pun, because eating its mail makes no sense.
A slip of the pen is regarded as a type of heterophemy, the unintentional use of an incorrect or inappropriate word or phrase in speech or writing. – Richard Nordquist