This is a JSON (or compatible with most language arrays) array that contains a list of subdomains that you want to reserve in multi-tentant applications.

Reserved-Subdomains.json

[
    "a",
    "aa",
    "about",
    "abuse",
    "access",
    "account",
    "accounts",
    "ad",
    "admin",
    "administrator",
    "administrators",
    "ads",
    "adserver",
    "adv",
    "affiliate",
    "affiliates",
    "alpha",
    "analytics",
    "api",
    "app",
    "apps",
    "archive",
    "asset",
    "assets",
    "atom",
    "auth",
    "auto",
    "autoconfig",
    "aws",
    "b",
    "b2b",
    "backup",
    "backups",
    "bb",
    "bbs",
    "bbt",
    "bd",
    "beta",
    "billing",
    "blog",
    "blogs",
    "board",
    "book",
    "bookmark",
    "bookmarks",
    "bot",
    "bots",
    "broadcast-ip",
    "bug",
    "bugs",
    "business",
    "c",
    "cache",
    "cal",
    "calendar",
    "careers",
    "cdn",
    "chat",
    "click",
    "client",
    "clients",
    "cloud",
    "cms",
    "cn",
    "code",
    "comment",
    "comments",
    "communities",
    "community",
    "connect",
    "contact",
    "content",
    "contributors",
    "control",
    "copyright",
    "corp",
    "cp",
    "cpanel",
    "create",
    "crm",
    "css",
    "cssproxy",
    "customize",
    "d",
    "dashboard",
    "data",
    "db",
    "dbadmin",
    "dc",
    "de",
    "delete",
    "delta",
    "demo",
    "design",
    "destroy",
    "dev",
    "devel",
    "develop",
    "developer",
    "developers",
    "development",
    "diagnostics",
    "direct",
    "directory",
    "diversity",
    "dmca",
    "dns",
    "doc",
    "docs",
    "dom",
    "domain",
    "domains",
    "dow",
    "download",
    "downloads",
    "e",
    "east",
    "e-mail",
    "edit",
    "edu",
    "email",
    "embed",
    "embedded",
    "en",
    "eng",
    "english",
    "enterprise",
    "es",
    "event",
    "events",
    "example",
    "exchange",
    "explore",
    "f",
    "facebook",
    "faq",
    "faqs",
    "favorite",
    "favorites",
    "fax",
    "fb",
    "fcx",
    "feed",
    "feedback",
    "feeds",
    "file",
    "files",
    "finance",
    "firewall",
    "form",
    "forms",
    "forum",
    "forums",
    "foto",
    "fr",
    "free",
    "friend",
    "friends",
    "fs",
    "ftp",
    "fw",
    "g",
    "gallery",
    "game",
    "games",
    "gate",
    "gateway",
    "ge",
    "general",
    "get",
    "gift",
    "gis",
    "git",
    "global",
    "gm",
    "gmail",
    "go",
    "google",
    "gov",
    "group",
    "groups",
    "guard",
    "guide",
    "guides",
    "health",
    "help",
    "home",
    "host",
    "hosting",
    "hostmaster",
    "hr",
    "html",
    "i",
    "icon",
    "icons",
    "id",
    "idp",
    "im",
    "image",
    "images",
    "imap",
    "img",
    "in",
    "inbox",
    "index",
    "info",
    "insight",
    "insights",
    "intel",
    "international",
    "intra",
    "intranet",
    "invite",
    "ip",
    "ipconfig",
    "iphone",
    "ipv4",
    "ipv6",
    "irc",
    "it",
    "jabber",
    "job",
    "jobs",
    "knowledgebase",
    "lab",
    "labs",
    "legacy",
    "legal",
    "library",
    "libs",
    "link",
    "links",
    "linux",
    "list",
    "lists",
    "live",
    "local",
    "localhost",
    "logs",
    "login",
    "loop",
    "m",
    "mac",
    "mail",
    "mailadmin",
    "mailer",
    "mailhost",
    "mailing",
    "mailman",
    "mailserver",
    "main",
    "manage",
    "map",
    "maps",
    "market",
    "marketing",
    "mass",
    "master",
    "media",
    "member",
    "members",
    "messages",
    "microsoft",
    "mirror",
    "mmc",
    "mms",
    "mobile",
    "monitor",
    "monitoring",
    "mood",
    "mrtg",
    "ms",
    "mssql",
    "mx",
    "my",
    "mysql",
    "nation",
    "national",
    "nav",
    "net",
    "nets",
    "network-ip",
    "new",
    "news",
    "newsletter",
    "next",
    "nl",
    "noc",
    "north"
    "ns",
    "ntp",
    "ntp1",
    "office",
    "official",
    "old",
    "oldmail",
    "omni",
    "one",
    "online",
    "oracle",
    "origin",
    "outlook",
    "owa",
    "p",
    "pages",
    "paid",
    "panel",
    "park",
    "partner",
    "partners",
    "pay",
    "payment",
    "payments",
    "paypal",
    "pbx",
    "pda",
    "pg",
    "pge",
    "pgs",
    "pgsql",
    "photo",
    "photos",
    "php",
    "phpmyadmin",
    "pics",
    "picture",
    "pictures",
    "plain",
    "pm",
    "policy",
    "pop",
    "pop3",
    "portal",
    "post",
    "postmaster",
    "pr",
    "press",
    "preview",
    "price",
    "prices",
    "principal",
    "privacy",
    "private",
    "pro",
    "prod",
    "product",
    "production",
    "products",
    "pro",
    "profile",
    "project",
    "projects",
    "promo",
    "proxy",
    "public",
    "purge",
    "qa",
    "quantum",
    "redirect",
    "region",
    "regions",
    "register",
    "relay",
    "remote",
    "report",
    "reports",
    "research",
    "reviews",
    "root",
    "router",
    "rss",
    "ru",
    "s",
    "sales",
    "salesforce",
    "sandbox",
    "search",
    "secure",
    "seo",
    "server",
    "service",
    "services",
    "setting",
    "settings",
    "sftp",
    "share",
    "sharepoint",
    "shop",
    "shopping",
    "show",
    "sip",
    "site",
    "sitebuilder",
    "sitemap",
    "sites",
    "sms",
    "smtp",
    "social",
    "software",
    "south",
    "sp",
    "spam",
    "speed",
    "speedtest",
    "sport",
    "sports",
    "sql",
    "ssh",
    "ssl",
    "sso",
    "st",
    "staff",
    "stage",
    "staging",
    "start",
    "stat",
    "stats",
    "static",
    "statistics",
    "stats",
    "status",
    "storage",
    "store",
    "stream",
    "streaming",
    "student",
    "style",
    "styles",
    "support",
    "survey",
    "system",
    "tag",
    "tags",
    "team",
    "teams",
    "tech",
    "temp",
    "terms",
    "termsofservice",
    "test",
    "testing",
    "the",
    "thumbs",
    "ticket",
    "tickets",
    "time",
    "tmp",
    "tool",
    "tools",
    "tos",
    "track",
    "tracker",
    "tracking",
    "train",
    "training",
    "travel",
    "travelers",
    "ts",
    "tv",
    "uk",
    "unfi",
    "up",
    "update",
    "updates",
    "upgrade",
    "upgrades",
    "upload",
    "us",
    "user",
    "username",
    "usernames",
    "users",
    "utc",
    "v",
    "vfc",
    "video",
    "videos",
    "vip",
    "visa",
    "vod",
    "voip",
    "volunteer",
    "volunteers",
    "vpn",
    "vps",
    "w",
    "w3",
    "wap",
    "web",
    "webconf",
    "webdisk",
    "webhook",
    "webhooks",
    "webmail",
    "webmaster",
    "west",
    "wifi",
    "wiki",
    "wm",
    "wnr",
    "wordpress",
    "work",
    "wp",
    "ws",
    "ww",
    "ww1",
    "ww2",
    "ww3",
    "www",
    "www2",
    "xml",
    "xmpp",
    "y",
    "yes",
    "yaml",
    "yum",
    "z",
    "zimmerbiomet"
]

This is a JSON (or compatible with most language arrays) array that contains a list of subdomains that you want to reserve in multi-tentant applications.

For example, you wouldn't want someone to use the subdomain email for their account, reserving the domain email.yourdomain.com for their account, instead of a more practical use like your company's email. There are many subdomains that you don't think of that you might want to use down the road, so it is good to have a list of subdomains that you don't want to give out to user accounts.

When creating a new account now you will check the requested (or generated) username against this list, and then check for uniqueness in your application (to make sure no other accounts are already using it).

Recommendation: I also, personally recommend restricting any account username to being > 4 characters. This way all short usernames can be created or reserved for your internal use. You can always abbreviate something in the future down to <4 characters and know that it will not interfere with user account subdomains.

thank you, this really helped me