Mail

Borderlands 3 has a mail system which allows players to receive items in-game. Rewards from the Borderlands 3 VIP program, pre-order bonuses, ECHOcast rewards, and in-game bonuses are all sent to the player's mailbox. Mail is only accessible while playing, and trying to access it from the main menu with be met with an error message.

There is a maximum inbox capacity of 25 messages. After that, new messages will push out old ones.

In-Game Rewards
The weapons manufacturers in Borderlands 3 reward users for brand loyalty. Whenever a player makes 100 kills using a company's weapons, they will receive a complimentary gun in the mail. Each gun comes with a short message that reflects the company's branding.

Players can also receive weapons and trinkets from individuals, such as Zer0 and Sir Hammerlock, for completing side missions.

Atlas
Atlas mail is delivered with the subject line "Reward, Reinforcement, and Retention Protocol", and each message ends with the company's motto: "ATLAS: Feel the Power of the Gods."

Messages that can accompany the guns:
 * Atlas and our customers share an immense responsibility: to continuously demonstrate unrivaled superiority; to establish and maintain order throughout the six galaxies; to distinguish between Gods and Men. The burden of this responsibility, on any other shoulders, might be too much. But not for you. / Our tester metrics indicate you recently eliminated one hundred enemies using Atlas weapons systems. The data from these engagements is invaluable to our continued research. As thanks, we're sending you a new, advanced Atlas prototype for your own use. / In the right hands, the gift of fire from the Gods can light the way for all mankind.
 * Atlas was founded with one idea in mind: to develop the most powerful, most technologically advanced, most profitable, best corporation in the history of mankind. So far, we think we've done a pretty good job. / But we never would have made it this far without users like you who believe in us along the way. Users who faced down one hundred enemies with an Atlas in their hands, and emerged victorious. / Your champion spirit embodies the soul of Atlas. / As thanks, and as a reminder of your continued committeemen to YOU, we're sending you a brand new Atlas weapon. Because when Atlas users are empowered, Atlas wins.

Dahl
Dahl mail is delivered with the subject line "Competency Rewards Program [CLASSIFIED -- PREMIUM CUSTOMER EYES ONLY]". Each message ends with the company's motto "VIRTUS. STABILITAS. FIDELITAS. DAHL" and the signature "Maj. H. H. MacPowell, Director of Contractor Services, 72nd Dahl Legion".

Messages that can accompany the guns:
 * Attention, Soldier! / In accordance with Dahl User Standards Regulations of Conduct, all User outfitted with Dahl proprietary technology are subject to random remote performance screenings. In light of your recent achievement, having registered ONE HUNDRED (100) CONFIRMED KILLS, DAHL HIGH COMMAND has updated your account with ONE (1) MERIT. / Additionally, you will find attached to this message a new weapon, the better to continue serving THE DAHL CORPORATION. Dismissed.
 * [CLASSIFIED BY DAHL OFFICE OF VALOROUS DISCRETION STANDARD DECLASSIFICATION SCHEDULE OF DAHL COMMAND 9211C] / After Achievement Report of Exemplary Battle Conduct Battle of [CODENAME REDACTED] [TIME REDACTED] - [NAME REDACTED] AKA "Recruit", encountered hostile [ENEMY REDACTED] in [LOCATION REDACTED] region. / After Recruit assessed hostile threat and designated primary target, Recruit opened fire with certified Dahl armament serial #[SERIAL NUMBER REDACTED]. / Following sustained fire, hostile threat was neutralized. / Intelligence office received dispatch at [TIME REDACTED] notifying that Recruit had neutralized ONE HUNDRED (100) hostiles using certified Dahl arms. / Per standard operating procedure, office is issuing notification of conduct to Recruit, as well as ONE (1) non-standard premium Dahl armament in recognition of Recruit's valor. / See attached.
 * Strength. Stability. Loyalty. / These are the bedrock upon which Stanton Dahl founded the Dahl Corporation. Recently, your registry was updated with your 100th kill using Dahl weaponry, demonstrating your adherence to these guiding principles. / The Strength to overcome your foes. The Stability to endure against overwhelming numbers. The Loyalty to stand with Dahl against our competitors. / Dahl recognizes your outstanding contributions, and would like to reward your service. / Find attached to this message one (1) Dahl firearm of superior quality intended for your use. / May it serve you as well as you have served Dahl.
 * ATTN / CLASS-A USER HAS COMPLETED RECURRENT ELIMINATION MISSION KILO ONE ZERO ZERO - ELIMINATE 100 ENEMIES USING DAHL WEAPONS AXIOS PROTOCOL ENGAGED: / >UPDATING USER DATABASE / >NOTIFYING DAHL OFFICE OF CONTRACTOR SERVICES / >SENDING USER DAHL ORDINANCE WEAPON / EFFECTIVE IMMEDIATELY

Hyperion
Hyperion mail is delivered with the subject line "Mandatory Employee Assessment [Satisfactory]". Each message is addressed to "Employee #" followed by an eighth-digit number. Each message ends with the company's motto "Hyperion: Empowering Entrepreneurs since the Corporate Wars" or "Hyperion: We Own You" and the signature "Jeffrey Damien Blake, President of Mercenary Relations and Tourism".

Messages that can accompany the guns:
 * This is an automated notification that, due to your consistent efficiency (100 eliminations), your account has been flagged as "potentially not mediocre". / For the duration of your reading of this message, you may take voluntary unpaid leave. / Additionally, as a test of your potential to handle increased responsibilities, please find attached to this message a Hyperion weapon. Technically, no further action is required on your part. / However, we trust you know what to do.
 * Hyperion wishes to [thank] you for your [contributions to] the corporation. Because you have [eliminated] [100] [competitors], it is with great [appreciate] we must [reward] you with [1] [Hyperion] [weapon]. / We hope you [have a nice day]. / Sincerely, / [Thank] You.
 * At Hyperion, we're always looking for employees eager to excel at any given task, who can cooperate with a flexible team, who aren't afraid to get their hands dirty. / Your manager referred your file for review, noting that you've eliminated 100 competitors using Hyperion's galaxy-class technology. / It's employees like YOU that show the best of what Hyperion can be. / Attached, you'll find an unscheduled bonus credited to your account: a premium Hyperion firearm, ready-to-use./ From all of us here at Hyperion, / Thank You.
 * Recently it has come to our attention that your performance in the field has consistently exceeded expectations. Our records show that you've eliminated 100 competitors. / Note that, as an at-will-contractor of Hyperion's Accounts Terminations department, you are entitled to a merit-based bonus which includes discretionary access to both a Hyperion Vice-Executive Tier firearm [see message attachment], and Level 2 Break Room Clearance at any Hyperion office. / If you have any questions regarding your assessment, bonus, or employment status, you may report to your nearest Accounts Services outpost for termination.

Maliwan
Maliwan mail is delivered with the subject line "Welcome", and each message ends with the company's motto: "Maliwan: Form and Function."

Messages that can accompany the guns:
 * If you're reading this, congratulations. Not only have you joined the elite and distinguished ranks of Maliwan by acquiring and operating Maliwan's top-of-the-line hardware -- you've been selected from among a pool of qualified candidates for Ultra Elite status. / By using Maliwan's elemental tech to kill 100 enemies, you've proven you don't just buy Maliwan -- you live it. / Maliwan users deserve the best, because they are the best. That's why we're sending you an exclusive, top-of-the-line Maliwan weapon. / Because what good is being the best if you can't prove it to everyone around you?
 * Not everyone is cut out to be a Maliwan user. It takes a fearless eye, a decisive hand, and an unerring sense of style. / You would know -- you've eliminated 100 enemies that couldn't handle the power and grace of Maliwan technology. / But you, you're different. / Stronger. / Better. / Special. / That's why we can send you this new, iconic Maliwan weapon -- because in your hands, it means something. / While other people turn to piles of ash, winners turn to Maliwan.

Moxxi
Players receive Moxxi-themed weapons in the mail after tipping her enough times in her bar on Sanctuary.

Players receive trinkets and decorations from Moxxi for hijacking COV radios. All of Moxxi's messages are simply signed with her name.

Trinkets

 * Floodmoor Basin: You've been good. Or at least good at being bad. Here's your reward.
 * Trinket received: Queen of Hearts

Sir Hammerlock
Players receive Jakobs weapons in the mail after killing beasts for Sir Hammerlock's Legendary Hunt challenges.
 * Lavendary Crawly: And now the putrid Crawly bloodline is ended. Hurrah and thank you.
 * Weapon received: Iron-Willed Longrider
 * Skrakk: For your feats of bravery in felling the beast known as the Skrakk, I hereby reward you with a deadly firearm!
 * Weapon received: Iron-Willed Marshall
 * Chupacabratch: A pestilence upon the hallowed shores of Athenas, it was! But you dispatched the Chupacabratch quite expertly!
 * Weapon received: Unflappable Cuttin' Scattergun
 * Chonk Stomp: A terrific showing! And what a hunt it was! You have my gratitude for this new reptilian trophy.
 * Weapon received: Dastardly Bowie Longrider


 * Jabbermogwai: It looks like someone fed this beast after midnight. But thanks to you, its head will now adorn my wall!
 * Weapon received: Round-Up Scattergun

Zer0
Players receive Hyperion weapons in the mail after killing targets for Zer0 in his Target of Opportunity challenges.
 * Handsome Jackie: Now Jackie is dead, / She will trouble us no more, / Rot in hell, kiddo.
 * Weapon received:
 * Judge Hightower: What a bastard, eh? / This is the fate of traitors, / To die by your hand.
 * Weapon received:
 * Heckle and Hyde
 * Weapon received: Powerhouse Powerplay

ECHOcast Rewards
Unlike other mail, weapons received from ECHOcast loot have an expiration date, which can be seen at the bottom right of the message. The subject line for this loot is "ECHOcast Viewer Rewards".
 * Congratulations, viewer! You're one of the lucky few selected for our loot-sharing lottery program! Please accept the attached digistructed copy of ECHOcast's loot, along with our thanks. Support from viewers like you is what makes ECHOcast possible. Be sure to thank your streamer with continued support, and keep watching for more rewards!

Shift Keys
SHiFT keys come with the subject line "Golden Key for Borderlands 3", followed by the number of keys available. The player must accept each key one at a time.
 * You have unlocked a Golden Key for Borderlands 3! You can use your Golden Key on the mysterious loot chest located on Sanctuary III to receive rare, powerful items! / Press 'Accept' to redeem the mail contents into your inventory.