The mailfish is light green with light yellow lips and wears a full mailman's outfit that is light blue with a matching hat. He also has thick light brown eyebrows and a thick light brown mustache and carries a brown mailbag around his shoulder.
The mailfish first appears at the very beginning of the episode "The Good Krabby Name." Mr. Krabs spots him walking by the Krusty Krab. He then takes a picture of him and puts that picture on the wall of customers who haven't eaten at the Krusty Krab yet.
The mailfish then appears at the end of the episode along with an angry mob trying to get to SpongeBob and Patrick. Mr. Krabs spots him and allows him to come in and takes him to the top of the Krusty Krab. Mr. Krabs celebrates having his very last customer to eat at the Krusty Krab while the mailfish looks confused.
According to Mr. Krabs, the mailfish is the last one percent of the population of Bikini Bottom to eat at the Krusty Krab.