- SpongeBob SquarePants
- Patrick Star
- Gary the Snail
- Sandy Cheeks
- Mermaid Man (cameo in a magazine)
- Barnacle Boy (cameo in a magazine)
- French Narrator
- Bikini Bottomites
- Fire fish
- Old Man Jenkins
- Priest (debut)
- Abigail Marge
- Eugene H. Krabs (cameo on a billboard)
- Patty Rechid (cameo)
The episode opens up with SpongeBob bored because Patrick is away. He then finds a Mermaid Man and Barnacle Boy comic lying on the floor and reads the section about pen pals. He then decides to write a letter, although Gary's slime goes all over it, making the word "frying" look like "flying."
SpongeBob is then seen waiting inside his mailbox a few days later and immediately goes to read the letter the pen pal sent. When SpongeBob reads it, he realizes the pen pal misinterpreted frying as flying, and then reads on and sees that he is dying. After thinking about how it could affect him, he decides not to break the news and write back with another lie.
Another few days later, SpongeBob receives the next letter, and it says that the pen pal wants to see him fly at the Bikini Bottom air show. Not knowing what to do, he goes to Sandy to seek help. She suggests learning to fly, which SpongeBob happily goes along with, but, when faced with the simulator, is not very good at it and breaks it while crashing into his pineapple house. It is the same when he actually flies, but Sandy decides that it is good enough.
At the air show, SpongeBob is there and comes across an old person in a wheelchair who he presumes is the "pen pal," but they actually turn out to be an old man choking on a Krabby Patty.
SpongeBob is then announced to be up next and gets on the plane, revising what he is going to do, before he is confronted by Steve, who is dressed as death.
SpongeBob then goes to take off, and Patrick is running nearby and reveals that he is the "pen pal," along with the other page of the letter. They both throw the letters up into the air, but they fly into SpongeBob's face, making him lose control and risk crashing many times until they eventually crash, and the fire department arrives.
SpongeBob and Patrick walk away with Patrick listing what else he would have wanted to see, and the episode ends with chaos at the air show with Sandy and the firemen putting out the fire.
|( ‣ ) Associated production music|
|( • ) Original music|
|( ◦ ) SpongeBob music|
‣ Hawaiian Cocktail - Richard Myhill [SpongeBob is bored]
‣ Vibe Q Sting - Nicolas Carr ["Oh, what's this?"]
‣ Arizona Fanfare - Jack Shaindlin [SpongeBob reading the Pen Pal article]
‣ Bikini Bottom Bound - Nicolas Carr, Sage Guyton, Jeremy Wakefield [SpongeBob writes a letter.]
‣ Victim 5 - Harry Lubin [SpongeBob's writing gets smudged by Gary]
• Hot Steel and Slide Licks (u) - Jeremy Wakefield ["Eh, it's just a little slime."]
‣ Bikini Bottom Bound - Nicolas Carr, Sage Guyton, Jeremy Wakefield [Mailman arrives]
‣ Drama Link (g) - Hubert Clifford [SpongeBob gasps]
‣ Dramatic Impact 6 - Ivor Slaney ["Dying!?"]
• Hot Steel and Slide Licks (j) - Jeremy Wakefield [SpongeBob cries]
‣ Unknown Track 25 - Nicolas Carr [Pen Pal's funeral]
‣ Taps - Pen Pal buried
‣ Fanfare (b) - Nicolas Carr ["Time to make Pen Pal's wish come true!"]
‣ Unknown Track 1 - Sage Guyton, Jeremy Wakefield [SpongeBob writes another letter]
‣ Dramatic Impact 2 - Ivor Slaney ["...so I can finally see you fly!?"]
‣ Dramatic Cue (g) - Ronald Hanmer [SpongeBob panics]
• Hot Steel and Slide Licks (r) - Jeremy Wakefield [SpongeBob trickles]
‣ Hot Steel and Slide Licks - Jeremy Wakefield ["Take these, they're clean."]
‣ Drama Link (c) - Hubert Clifford [SpongeBob struggles to say Sandy he lied]
‣ Drama Link (e) - Hubert Clifford ["I lied!"]
‣ The Fruitcake Vendor - Nicolas Carr, Barry Anthony [Sandy asks SpongeBob to explain]
‣ Sponge Monger - Sage Guyton, Jeremy Wakefield [SpongeBob rapidly explains]
• Hot Steel and Slide Licks (v) - Jeremy Wakefield ["Really?"]
‣ Unknown Track 72 - Video game music
• Hot Steel and Slide Licks (e) - Jeremy Wakefield [Sandy notices SpongeBob's gone]
‣ Dignity - Peter Yorke [Wooden plane takes off]
• Hot Steel and Slide Licks (f) - Jeremy Wakefield ["Did I do it?"]
‣ Victory Parade - Ronald Hanmer [At the air show]
‣ Unknown Track 29 - SpongeBob going over what to do
‣ Shock (f) - Dave Hewson [Grim reaper next to SpongeBob]
‣ Gator - Steve Belfer [A scythe salesman is revealed.]
‣ Hot Steel and Slide Licks - Jeremy Wakefield ["No, it's still not that."]
‣ Adventure Fanfare 1 - Harry Bluestone, Emil Cadkin ["You'll be, uh...just fine, yeah!"]
‣ Air Power - Sidney Sager [Plane takes off]
‣ Grass Skirt Chase - Sage Guyton, Jeremy Wakefield [Patrick reveals to be SpongeBob's pen pal]
‣ Slipping and Sliding Stooges - Nicolas Carr, Sage Guyton, Jeremy Wakefield [SpongeBob loses control of the plane]
‣ Bloodbath - Harry Lubin [Plane breaks down]
‣ Nude Sting - Nicolas Carr [Empty fuel tank]
‣ Cream Pie - Sage Guyton, Jeremy Wakefield [ending]
- As of June 21, 2019, The Internet Movie Database (IMDB) gives this episode a rating of 8.3/10 based on 194 ratings by users. TV.com users give this episode a rating of 8.9/10 based on 8 votes.
- The one-cent stamp from "Kracked Krabs" can be seen on the top-right corner of the title card for this episode.
- This is the second episode where SpongeBob wants to fly. The first is "The Sponge Who Could Fly."
- However, he is able to fly successfully in this episode, unlike in "The Sponge Who Could Fly."
- This episode is similar to "Dying for Pie," because in both episodes, a character wants to do something for someone because of a misunderstanding that involves the other person dying.
- This is the third episode where a time card appears more than once. The first is "Sun Bleached" and the second is "A Friendly Game."
- The title comes from Gary smearing his slime on SpongeBob's mail letter.
- It also comes from the phrase "snail mail," which is what some users of the Internet use to refer to the standard postal service, as it is slower and less reliable than e-mail.
- Gary does not deliver the mail, even though an early promotional image showed him doing so.
- Unlike in "Chocolate with Nuts," the mailfish is not scared when he opens a mailbox and sees SpongeBob's face.
- When SpongeBob is about to write a letter to his pen pal, he is shown sharpening a pencil with his mouth like a pencil sharpener. This is similar to how DoodleBob sharpens the Magic Pencil with his own mouth in "Frankendoodle."
- The red airplane slightly based on Soviet World War 2 fighter, Polikarpov I-16.
- Old Man Jenkins is known as "Frail Fish" in this episode.
- The plane that SpongeBob crashes into during his flight heavily resembles a real-life airliner: the Airbus A320, but the rear fuselage and tail look like that of a Boeing 737, albeit with a smaller vertical stabilizer.
- This is one of the first appearances of a realistic-looking airliner in the show.
- This episode premiered six years after SpongeBob Marbles & Slides was updated for the first time and three years after Plankton's Robotic Revenge was released.
- This episode premiered in Canada 11 years after "Mermaid Man & Barnacle Boy VI: The Motion Picture" premiered and six years after SpongeBob Marbles & Slides was released.
- The running gag of Sandy offering SpongeBob a pair of underwear when he is nervous is a reference to "Oral Report," where Sandy gives a pair of underwear with goggles to SpongeBob that make him see people in their underwear. She gives this because according to her studies, it makes a person less nervous talking in public when they see people in their underwear. This is because SpongeBob has an oral report at Mrs. Puff's Boating School.
- This is the only season 9 episode to use the APM track "Hawaiian Cocktail."
- SpongeBob writes his name as "Spongebob Squarepants," when grammatically it should be "SpongeBob SquarePants."
- When the ice cream splats on the firefighters and Sandy, the ice cream is on Sandy's face even though she is wearing her helmet.
- When SpongeBob is following Patrick with the plane, the same fish can be seen in the stands multiple times.
- When Patrick fills the plane, a gas port is seen. In the next shot, it is not there.
- In the shot where SpongeBob crashes the "Flight Trainer," he is not seen in the seat.
- In the scene where SpongeBob tries to fix the flap, there isn't one on the other wing. Also in the next scene, the broken flap disappears.
- Sandy offering SpongeBob a pair of underwear whenever he is nervous.