MultiMailWebmail
An email service you use through a web browser — Gmail, Outlook.com and Yahoo Mail are the big three. Your messages live on the provider's servers and the interface is a web page, which is why webmail works on any device but traditionally lives inside a browser tab.
Email client
A standalone program that downloads or synchronizes your messages onto your computer, usually over IMAP or POP3, and shows them in its own interface — Thunderbird, Outlook (the desktop program) and eM Client are classic examples. The client keeps a local copy of your mail and replaces the provider's web interface with its own.
Webmail wrapper
A desktop app that loads the real web version of your email service inside its own window instead of re-implementing an inbox. Nothing is synced to third-party servers — you sign in to the provider directly, and the wrapper adds desktop conveniences such as native notifications, isolated sessions per account and keyboard switching. MultiMail and Kiwi for Gmail are examples.
IMAP
Internet Message Access Protocol — the standard way email clients synchronize messages with a mail server. Mail stays on the server; the client mirrors folders and read/unread state across devices. IMAP is what a classic email client uses under the hood, and what a webmail wrapper deliberately avoids by showing the provider's own web interface.
POP3
Post Office Protocol version 3 — an older retrieval protocol that downloads messages to one device and, in its default setup, removes them from the server. It predates the multi-device world; today IMAP or the provider's web interface is almost always the better choice.
SMTP
Simple Mail Transfer Protocol — the protocol used to send email. When an app asks for an SMTP server, it wants to know where to hand over your outgoing messages. Webmail users normally never see SMTP settings because the provider's web interface handles sending itself.
OAuth
The sign-in standard ("Sign in with Google/Microsoft") that lets an app access your account without ever seeing your password. Google has phased out plain-password access for email apps in favour of OAuth, which is why some older email clients periodically break with Gmail while browser-based sign-ins keep working.
PWA (Progressive Web App)
A website installed to behave like an app — Chrome and Edge can "install" Gmail so it opens in its own window with its own taskbar icon. A PWA is still the browser underneath: it uses the browser's cookies and one profile, so it inherits the browser's limits with multiple accounts and notifications.
Unified inbox
A single merged view showing messages from several accounts together, typically offered by IMAP email clients. The opposite approach keeps every inbox separate but one keystroke away. Merging is convenient for triage; separation avoids sending from the wrong address and keeps work and personal mail visually distinct.
Session isolation
Keeping each account's cookies, cache and sign-in state in its own container so accounts cannot see or overwrite each other. Browsers share one cookie jar per profile, which is why adding a fifth Gmail account tends to sign another one out; isolated sessions are how desktop apps run many accounts of the same provider side by side.
Browser profile
A separate identity inside Chrome or Edge with its own cookies, extensions and windows. One profile per email account gives real session isolation for free, at the cost of one browser window per account and notifications that only fire while the browser is running.
Email forwarding
A rule at the provider that automatically resends incoming mail to another address. Forwarding everything into one main inbox is a zero-software way to "combine" accounts, but replies still come from the main address unless you also configure send-as aliases, and the setup lives per provider.
Desktop notifications
System-level alerts (Windows toasts) that appear whether or not the app is focused. Browser tabs can only show notifications while the browser runs and the site's permission is granted; native Windows apps register with the notification centre directly, which also lets Focus Assist and Do Not Disturb rules apply to them properly.
Focus Assist / Do Not Disturb
The Windows feature (called Focus Assist in Windows 10, Do Not Disturb plus Focus in Windows 11) that silences notifications on a schedule or during full-screen use. A very common reason "my email notifications stopped working" — the messages arrive, but Windows suppresses the toasts.
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