An email client for multiple accounts, or one window each

Four addresses, one Mac, and the message that mattered arrived in whichever account was not on screen. That is the state most people are in when they start looking for an email client for multiple accounts. The search usually returns lists of apps ranked by feature count, which is the wrong axis. Nearly every serious mail client on macOS supports more than one account. What separates them is where the limits sit, which protocols they speak, and whether merging the accounts solves the problem or creates a new one.

What follows is the shape of the decision: the three different things vendors mean by multi-account support, what the current free tiers actually allow, the protocol question that quietly rules out some options, and the point at which the mail client stops being the thing that needs changing.

Three different features get sold as one

"Supports multiple accounts" covers three capabilities that are worth separating before comparing products, because a client can be strong at one and weak at another.

The first is account capacity: how many mailboxes can be connected at all, and of which types. This is the least interesting of the three, because it is rarely where anyone gets stuck. Spark lists unlimited email accounts on its free plan. Canary Mail lists unlimited mail accounts on its free plan as well. Apple Mail, included with macOS, takes accounts through Mail > Add Account, where iCloud, Google, Exchange and other providers are offered from a list. Thunderbird, which is free and donation funded across Windows, Linux and macOS, has no account ceiling either.

The second is the merged view: whether the inboxes can be read as one list. Almost all of them do this now, and almost all of them let individual accounts be excluded from it. The merged view is a reading convenience. It changes how many places have to be checked, not how mail is filed or sent.

The third, and the one that decides whether a setup survives contact with real work, is identity separation: how clearly the app shows which account a reply will leave from, and how hard it is to send from the wrong one. Colour coding, per-account profiles and separate notification schedules all belong here. Feature lists tend to bury this under the merged inbox, which is backwards. Someone juggling a personal address and a freelance address wants the merge. Someone juggling two employers wants the separation.

Deciding which of those three is the actual complaint removes most of the candidate list immediately.

What the current free tiers allow

Free tiers in this category are not trial versions with a countdown. Several are permanent, and the paid upgrade buys features rather than access. The table below reflects each vendor's own published terms.

Client	Cost	Account limit on free	Paid tier
Apple Mail	Included with macOS	No stated limit	None
Thunderbird	Free, donation funded	No stated limit	None
Spark	Free plan at $0	Unlimited email accounts	Plus $10 per month, or $99 per year
Canary Mail	Free forever at $0	Unlimited mail accounts	Growth $36 per year, Pro+ $100 per year
Mimestream	14-day trial, no card	Trial only	$4.99 per month, or $49.99 per year

Two details in that table matter more than the headline prices.

Canary Mail's free plan includes the unified inbox and unlimited accounts, but caps supported devices at two. Growth and Pro+ raise that to five. So the free plan is generous on mailboxes and tight on machines, which is the opposite of how free tiers usually work. Anyone with a MacBook, an iMac and a phone hits that ceiling before hitting any account ceiling.

Mimestream has no free tier at all. It offers a fully functional 14-day trial with no credit card required, and after that a subscription is the only option. The vendor states plainly that a one-time purchase is not available and that the app is not sold through the App Store. The Individual plan covers all Google accounts, allows use on up to five devices, and includes sharing with immediate family in the same household.

Spark's free plan covers unlimited accounts and its Smart Inbox, with the paid tiers adding AI features and team collaboration rather than raising account limits. The annual price is $99 for Plus against $120 billed monthly, and $199 for Pro against $240 monthly.

Protocol support rules out more candidates than price

The least visible difference between these apps is the one most likely to end the search early.

Mimestream is built on the Gmail API rather than IMAP. That choice is why it handles Gmail labels with colour coding and visibility settings, manages server-side Gmail filters from inside the app, uses Gmail's own inbox categories, and runs searches through Gmail's search engine. It also means the app connects to Google accounts and nothing else. Anyone whose four addresses include one on Exchange or a self-hosted IMAP server cannot use it as the single client. It requires macOS 12 Monterey or newer.

IMAP clients sit at the other end of that trade. Thunderbird, Apple Mail, Spark and Canary all speak IMAP and therefore accept almost any provider, at the cost of mapping Gmail's label model onto folders, which never lines up exactly. A message with three labels becomes a message in three folders, and archiving behaves differently from the way it behaves in the Gmail web interface.

The practical test is short. If every account is a Google account, a Gmail-native client removes a category of friction that no IMAP client can remove. If even one account is not Google, the choice is between a generic client for everything or two clients side by side, and two clients side by side reintroduces the switching that started the search.

Notifications are where a multi-account setup usually breaks

Adding four accounts to one app multiplies the number of interruptions by four unless the notification settings are changed on the same day, and almost nobody changes them on the same day.

The problem is not volume alone, it is that the accounts have different urgency profiles. A client address that sends two messages a week deserves a sound. A billing address that sends forty receipts a month does not. When both are wired to the same notification, the notification stops carrying information, and the usual response is to turn all of them off. At that point the mail app has been reduced to something that has to be opened and checked manually, which is where the day started.

Vendors have started treating this as a per-account setting rather than a global one. Mimestream's Profiles keep work and personal accounts separate and allow a custom notification schedule per account, so a work address can go quiet outside working hours while a personal one stays live. The same profiles can be tuned to a macOS Focus, which means the operating system's own state decides which accounts are allowed to interrupt. Canary Mail exposes custom alerts and push notifications on its free plan, with more granular customisation on paid tiers.

The setting to look for when comparing clients is therefore not "does it have notifications" but "can notifications be set per account, and can they be set on a schedule". A client that only offers one global switch will end up switched off.

There is a second-order effect worth naming. Once notifications are tuned per account, the merged inbox becomes considerably safer to use, because the accounts that were going to make the merged list unreadable are the same accounts that were going to make the notifications useless. Fixing one fixes most of the other.

A merged inbox does not fix attribution

Merging inboxes solves the checking problem. It does not solve, and can worsen, the sending problem.

In a per-account view, the mailbox is visible before the reply is written, so the sending identity is set by context. In a merged view that cue disappears and the sending address becomes a field to notice rather than a fact about where the reading happened. A reply that leaves under the wrong address is a trivial technical event and an awkward social one, and it gets more likely as the merged list gets busier.

The countermeasures vendors offer are real but partial. Mimestream assigns a unique colour per account so messages and labels associated with it are identifiable at a glance, and its Profiles feature keeps work and personal accounts separate with their own notification schedules, including behaviour during a macOS Focus. Canary Mail offers custom alerts and custom thread actions. Colour is better than no signal. It is still a visual convention that has to be read correctly at speed.

For accounts that must not be confused, the reliable move is to leave the sensitive one out of the merged view entirely and keep it as its own entry in the sidebar. That costs one extra click per check and removes the whole class of mistake. Trading a click for a category of error is almost always the right trade.

Mail is rarely the only account that doubled

There is a reason this search often ends with a new mail client and the same feeling of fragmentation a month later. Mail is the account that doubled first and the one that is easiest to see, but it is seldom the only one.

The same person with four mail addresses generally has two Slack workspaces, two Notion logins, two GitHub accounts, several calendars, and separate billing on a handful of web tools. A mail client is scoped to mail by definition. Everything else lives in a browser, where identity is held in a cookie jar, and a single browser profile can hold only one signed-in session per service at a time. That is why a perfectly configured mail client can coexist with a workday that still involves logging out of one Notion account to reach another.

The tools built for that half of the problem are a different category. They give each web app its own window and its own session store, so two accounts on the same service can stay open side by side. Free tiers here are narrower than in mail. Shift offers a free plan with five Spaces and ten apps per Space, with its Advanced tier at $199.99 billed annually. A feature comparison is the quickest way to see which of those windows-and-sessions capabilities matter, and the list of supported apps is the quickest way to check whether the specific services in use are covered before installing anything.

Worth stating plainly: this is an addition to a mail setup, not a replacement for one. A mail client indexes and searches mail better than a web view of Gmail ever will. The browser side handles the accounts a mail client was never going to reach.

What to change first

Start with the cheapest experiment. In whatever client is already installed, exclude the noisiest account from the merged view, give every remaining account a colour, and leave it alone for a week. That settles whether mail was the bottleneck before any money is spent.

If the switching continues because the other half of the day is also signed in twice, the unit that needs to change is the window rather than the mailbox, and SpaceDeck is built around that unit. The pricing page shows the free plan's limits, which is the fastest way to judge whether the step is worth taking at all.