Mail

Mail is a type of item in Undertale Yellow, usually given by Mail Whale. Clover can read it by going to the in-game menu and pressing the "MAIL" option. A letter's name is white to indicate it is unread and turns gray once it has been read. Clover is also given the option to pin mail, which always keeps it at the top of the mail list and turns its name yellow.

In addition to regular mail, spam mail has a small chance to be added to the unclaimed mail inventory whenever regular mail is added. Other papers that are not mail can also be added to the mail inventory.

Normal Mail

This is mail that Clover obtains from Mail Whale under certain conditions, usually from befriending monsters.

Name	Content	Stamp	Obtaining	Notes
Intro Letter	Come new friend, right here to our space! Whether you roam or stay in one place! We hope you have friends with fun letters to send, and always a smile on your face! Here's to more mail without any stress! Hope to see you again! The UGPS		Given by Mail Whale in Snowdin
Mo Letter	If you're reading this, it means you had the pleasure of meeting me. I'll make this snappy. You're not gonna believe it. I'm selling a new, premium product for HALF OFF. I know what you're saying, "I would gladly pay full price for your products."I appreciate that, I really do. But this ain't the time for high prices. Just find my stand and I'll give ya the juicy details. Huh? Where is my stand? I don't even know myself. Should probably go find that. Good luck! -Mo		Given by Mail Whale in the Dunes
Slurpy Letter	Greetings, my savior and fond acquaintance. I would like to extend further gratitude for your assistance.If it weren't for you, my papillae would surely be permanently attached to that pole. Thanks to you, I made it home in time for supper. I must say, Mother really outdid herself this time! The food was exquisite! Many thanks! Sincerely yours, -Slurpy		Given by Mail Whale after Martlet's battle after completing Slurpy's quest
Shufflers Letter	To our latest Shufflers recruit: Toast here. There's someone out in the wild that we forgot to warn ya about. This scruffy fella with a blue hat. Don't interact with him or support his endeavors. I won't tell ya why cause this letter reads way cooler as a mystery. Now, I'll let Swig finish this. He gets upset when he misses out on writing letters. Yeah, upset. -Swig		Given by Mail Whale in Oasis Valley	The name "Swig" is replaced with "Dave" if the Fun Value is 1.
Dalv Letter	Greetings, Clover! Life has been a treat since we last saw each other. I packed up all of my belongings and set out for Snowdin. I recently found a nice place to settle down. I think you'll like it! Oh! And all of the neighbors moved out with me.I'm not too sure where each one went, but I know they are doing well. I'm also taking art lessons from Penilla now. She gave me the cold truth and said my art needed lots of improvement. It stung at first, but then I remembered that you should always aim to improve yourself. Ah. Look at me rambling again. I hope the mail service doesn't charge extra for that. It was nice to talk to you again! Even if it is over written text. Please visit me in the future! Life is getting a lot better, -Dalv		Given by Mail Whale in Sunnyside Farm; Pacifist Route only
Starlo Update	Howdy, Clover! It's yer favorite sheriff, North Star, with an important update! I did some soul searchin' while staring directly at the shiny stone on top of the Mines. After recovering from temporary blindness, I shamefully approached my posse. Well, I'll spare ya the gruesome details (me cryin') but in the end, they forgave me. So the Feisty Five are back! Now twice as sensitive to everyones[sic] feelin's! When we returned to town, Ceroba and Dina had set up a party in the Saloon - which was great[sic] I really wish you were still here, but I SUPPOSE you deserve yer freedom ;) Anyway, it's all good, so don't mosey 'round worryin' 'bout me or nothin'. I do have the tendency to occupy around 60% of someone's brain after they meet me... But I reckon it's time to let go. Happy trails! - North "Starlo" Star		Given by Mail Whale in at the Steamworks - Commons station if Starlo was spared; Neutral Route only
Martlet's Letter	To: Clover (who's hopefully alive) Meet me on the roof of UG Apartments as soon as you can. There's something on my mind. - Martlet of the Royal Guard (Snowdin Division)		Delivered automatically by Mail Whale in the Steamworks (or just before Hotland, if the Pacifist or Genocide Route is aborted in the Steamworks); Neutral Route only	This cannot be dropped. In the room before Axis's battle, Flowey replaces this letter with the Missing Poster.
Slurpy Letter 2	Hello again, dear comrade! I hope this letter finds you in the very picture of health. I heard word that you were venturing near the vicinity of Hotland. Being that the resting temperature in that region is so high, I have included one premium Snowdin snow sphere. I hope it keeps you at an ideal temperature throughout your journey. Next time you are in Snowdin, feel free to drop in. Mother will surely prepare you a palatable meal. Sincerely yours, -Slurpy (The letter and envelope are very wet.)		Given by Mail Whale in Hotland after completing Slurpy's quest
MAIL???	1001001 100000 1000100 1001111 100000 1001110 1001111 1010100 100000 1001011 1001110 1001111 1010111 100000 1001000 1001111 1010111 100000 1010100 1001111 100000 1010011 1000101 1001110 1000100 100000 1001100 1000101 1010100 1010100 1000101 1010010 1010011 101110 100000 1001000 1000101 1001100 1010000 100000 1001101 1000101 101110 - Axis		Given by Mail Whale in Hotland if Axis was spared	The mail is written in binary code and when decoded with ASCII or UTF-8 translates to "I DO NOT KNOW HOW TO SEND LETTERS. HELP ME.".
Ceroba (Important)	Hey. We don't know each other very well but ever since you left the Wild East, I've been pacing around in my head about your journey and everything surrounding it. Wherever you are, I fear your situation will grow dangerous. Far more than it already has. By now, I assume you've heard about the King. Well, each fallen human who has encountered him in the past hasn't survived. As skilled as you are, I don't believe you would either. I understand why you would want to confront him (believe me, I have my reservations as well), but perhaps it isn't the wisest path forward? I don't know what you should do, nor am I going to act like I currently have any influence over your destination, but your original plan - avenging the humans, escaping the Underground, whatever it may be... It's impossible. I'm sorry. A warning is the best I can do. - Ceroba		Given by Mail Whale in Hotland if Starlo was spared; Neutral Route only
Starlo (Urgent)	Hey, Clover. Something's up. I made up with the posse as planned. All was going well, but then I began worrying about you and Ceroba. That's when I got the idea to break into Ceroba's old house and spruce it up to celebrate her and Kanako's eventual return. Well, when Ed was sweeping around, he found some kinda secret room. Seems like it belonged to Chujin. We didn't have time to dig into its content but all I know is it worried us both. You may be in danger. Then again, maybe not. Just... come back to the Wild East for now. I can only hope this letter reaches you in time. - Starlo		Given by Mail Whale after being taken back to the Wild East after defeating Axis; Pacifist Route only
Resort Letter	Hello, appreciated guest! We greatly enjoyed your company at The Honeydew Resort (Snowdin Establishment)! You can always count on us for quality time with the whole family! From our relaxing hot spring, to our live music, there's a little something for everyone! We hope to see you again, anonymous citizen of the Underground! -The Honeydew Family		Unused	Might have been intended for for Clover after their visit to the Honeydew Resort.

Spam Mail

Clover has a chance to receive spam mail whenever any item enters their mail bag, including when said item is not from Mail Whale. Clover can only obtain one spam letter per delivery, and they can receive the same spam letter multiple times.

They initially have a $\frac{1}{10}$ (10%) chance to receive a spam letter, which goes up to $\frac{1}{9}$ (11.1%) when they receive a letter and do not receive spam, then $\frac{1}{8}$ (12.5%) and so on. If they receive a spam letter with their mail, the chance falls to $\frac{1}{30}$ (3.33%), which changes to $\frac{1}{29}$ (3.45%) when they fail to receive spam, and so on. This chance can change multiple numbers at a time if they obtain multiple letters from Mail Whale at once. However, loading a SAVE, either from loading after dying or reopening the game, always resets the chance of receiving spam to $\frac{1}{10}$ (10%), making these calculations often irrelevant.

Name	Content	Stamp	Notes
Spam Letter 1	Hey, you! Are you wanting to help society? Don't know where to start? Well here's the: Top Ten Reasons to Join the Royal Guard! 10 - Awesome training courses! 9 - A shiny badge! 8 - Your own area to guard! 7 - A leather-bound protocol guidebook! 6 - Free space! Insert your own here! 5 - A weapon of your choice! 4 - Bragging rights! 3 - Free health insurance! 2 - Being more intimidating than before! 1 - Your own battle-ready uniform!! So what are you waiting for? Sign up today! Disclaimer: The Royal Guard is a serious job with life-threatening possibilities. This list was created for promotional purposes only. The Royal Guard is not liable for any promises made in this list.		This appears to be a spam letter advertising for the Royal Guard.
Spam Letter 2	Have you ever found yourself stranded in the desert, wishing you had an air-conditioned room to relax in? Well look no further than Cafe Dune! The most modern facility in the Dunes! Try out premium lattes or game it up in our state-of-the-art arcade! It's all right here at Cafe Dune! Located in Oasis Valley - See you soon!		A spam letter for Café Dune in Oasis Valley, which can be visited in-game.
Spam Letter 3	The ultimate question:What are the ideal proportions for lemonade? It is a mystery that has boggled all manner of monsters since Surface days of yore. It has bested generations of royal scientists and yet has remained elusive... Until now! Behold! The perfect ratio! 22% water 22% sugar 41% lemon juice ????????????? Want to find out that last ingredient? Well why not subscribe to It's A Lemon Monthly! Have the perfect lemonade recipe delivered to your door: Every. Single. Month. What are you waiting for? Only 18,300g for a three year subscription! Order now, now, NOW!		The unknown ingredient would be at 15% percent. Lemonade is usually only made with three ingredients: water, a sweetener, and lemon juice. The fourth ingredient is either an additional sweetener, carbonation, or ice. Humorously, since the order is specifically for receiving a "perfected" lemonade recipe over the course of three years, there is technically no point to receive that same recipe again.
Spam Letter 4	hi.......... please visit blook acres in waterfall, if you want..... we have snails..... they're neat........ ......bye.		The mail seems to have been written by Napstablook from Undertale. It mentions the Blook Acres area in Waterfall.
Spam Letter 5	If you're a foxy monster looking for love, look no further than yours truly! I'm an elite athlete with more G than I know what to do with. My IQ is so large, I could shatter the barrier just by staring at it. Regrets? My only regret in life is that I don't own a dumbbell heavier than 150kg. I could go on for eons, but enough about me. Write your number here and send this letter back if you want your world changed! __________
Spam Letter 6	Hello. This is the Royal Treasury notifying you that you definitely owe us 700G. Monsters must pay taxes to King ASGORE as of right now. I hear you getting all flustered but I assure you that I am correct. Now, insert the G into the envelope and return this letter or......Or else you get a life sentence without a trial. Yup.		Based on the tone of the wording and claims made, this is probably a scam and was not actually written by the Royal Treasury.
Spam Letter 7	The monster life can be stressful, we all know that. Wouldn’t you like to have a taste of Surface life? Well here in the Wild East, we pride ourselves on being the most authentic experience you'll find in the Underground! Located east of Oasis Valley - Stop on by, partner!		This is a spam letter for the Wild East, which can be visited in-game.
Spam Letter 8	Hello Underground friend, and thank you for taking the time out of your busy schedule to read this message. We here at the Society for Monster Health (SMH) are reaching out for support in our noble mission of putting an end to unsolicited spam mail. This unwanted clutter is an extra stress and possible danger to the mental state of monsters everywhere, in addition to putting needless physical strain on our poor mail monsters. Please join the fight against this wasteful spam mail by signing up for our petition today!		Ironically, this is of course, spam mail.
Spam Letter 9	Looking for a job? Here at Mining Co. we hire just about anyone who applies! Criminal past? Doesn't matter. Criminal future? Doesn't matter! We want everyone to feel secure in our cave away from home! So what are you waiting for? Apply today and help society! (Disclaimer: Not liable for any work-related accidents that may or may not occur.)		This is spam mail for the East Mines.

Other

Besides mail, specific items enter Clover's mail bag instead of their inventory. Most of these are papers or similar.

Name	Content	Stamp	Obtaining	Notes
Steamworks ID	Designed by player	N/A	Created in the Chemistry Lab; Neutral Route only	This cannot be dropped. Also see Steamworks ID.
Mixin' It Up! (Essay)	MIXIN' IT UP - By Dr. Rob Entering the field of chemistry can be tough. Maybe you never went to college. Maybe you find it hard to grasp complex equations. Maybe you were kicked out of your highschool science class for "developing poison during school hours." We're all different, but we all share one similarity: magic. It's easy to rely on magic in the in the day to day, but have you ever wondered what it would be like to live... without it? What would we do if we couldn't light a fireplace with a snap of our fingers? Spawn weapons out of thin air? Use wings to soar above the trees? Sleep? That's where science comes in! Nature's magic. Elements, or "compounds" make up most of the Underground as we know it. When you combine two or more compounds you can create amazing things. For example, by taking the compound "Oxygen" and SMASHING it together with two "Hydrogen" compounds, you get "Dihydrogen Oxide," also known as "water" (catchy name, right?) Here, you try: Let's say you want to melt through a high-security safe to become rich... hypothetically. The solution you would need is called "Hydrochloric Acid" which involves the two compounds _____ and _____. Fill in the blanks to empty the banks :) D- Unfocused and rushed. Why did you write a worksheet problem in a reflective essay?	N/A	Found in a trash can in the Steamworks Chemistry Lab	The actual chemical name of water is "dihydrogen monoxide", but "dihydrogen oxide" is also correct. The essay mentions pyromancy and weapon summoning through magic, which appear to be references to both Toriel and Undyne. A reflective essay is a type of essay where the author reflects on their past experiences and how those experiences changed them. Based on the contents of this essay, the writer, Dr. Rob, is bad with math, has never went to college, was expelled from science class for chemically synthesizing poison, and attempted to create hydrochloric acid to rob a safe.
Missing Poster		N/A	Obtained in the Steamworks, in a room just before where Axis is fought, before a dialogue with Flowey; Neutral Route only	Flowey can be seen disappearing behind Clover in the room before Axis, which causes Martlet's letter to be replaced by the poster. This implies that Flowey discreetly gave the poster to Clover to remind them of their goal. The game does not notify of this, so the player is not likely to notice it right away. This is the same poster that Clover loses after falling down into the Dark Ruins.
Bullet Points	The Helper-Bot Guidelines: 1. Every manufactured bot must have a practical function installed. A purpose for being: (Cooking, cleaning, agriculture, etc). 2. Bots should have tiers of emotion to better integrate into society. Coding a personality into each one is recommended. It makes them more personable/easy to be around. 3. All bots are to have a strong connection with living things: (Their creators, average monsters, other bots, etc). If deprived of this, some may become easily agitated and restless. Others may be unfazed. Depends on the model. 4. If a bot acts out of line or malfunctions, they are to be shut down. Typically, a hard reset will do the trick. Termination is a last resort. If a shutdown isn't possible, they can be coaxed back to their normal state. 5. Absolutely NO bots are allowed outside the Steamworks at this time. Until King ASGORE is ready to begin mass production, this project is classified. 6.Most of all, have fun :)	N/A	Obtainable by checking the trash can in the office room in the Steamworks; Pacifist Route only
PSA	Dear citizens of the Underground: We are calling for fallen down monsters to be sent to Hotland for important scientific research. Should you choose to participate, your loved ones will be treated with utmost respect, their condition heavily monitored, and you regularly notified of their status. This is a chance for tragedy to be turned into opportunity. For monsterkind to finally see the light of the Surface thanks to its citizens' invaluable bravery and sacrifice. For your consideration, Royal Science Division		Found in Ceroba and Chujin's bedroom drawer in the Ketsukane Estate	This letter seems to correspond to the Determination experiments carried out by Dr. Alphys in Undertale.

Trivia

• The only mail obtainable on the Genocide Route are the Intro Letter, Mixin' It Up! (Essay) and Spam Letters, since Mail Whale stops appearing after the kill count for Snowdin is exhausted.
• In the Snowdin trailer, the mail feature was revealed for the first time. Three mail messages were used as an example: a slightly different version of the Intro Letter, an excerpt from Wikipedia's Cowboy article, and a variation of Undertale's introduction screen, saying: Wong ago, two waces wuwed uwv Eawth: HUMANS and MONSTEWS. Ony day, waw bwoke out between the two waces. Aftew a wong battwe, the humans weww victowious. They seawed the monsters undewgwoundwith a magic speww.
• If Clover only has one letter, they can pin and then drop it to create a glitch where the pinned spot is blank but still interactable. Even if Clover unpins the letter or picks up more mail, the blank spot persists. When read, it displays the words "Mail Text" and the default stamp next to it.