Evaluating AI Email Tools for Multiple Mailboxes and Domains

One person, four mailboxes: a work Gmail, a personal Gmail, an Outlook for a side company, and an IMAP box on a legacy domain that will not die. The generic AI-email guides do not answer the question you actually have, which is not whether the tool has an AI assistant but whether that assistant behaves like four different people when you need it to.

This is the evaluation checklist for that decision. Six criteria that decide the purchase, a template you can score two finalists on in a trial, the red flags that end an evaluation early, and an honest note on where AI Emaily fits and where it does not. We build AI Emaily, and one of the six criteria is one we lose points on.

The short answer#

Check per-account autonomy and rules, per-identity voice, send-as and alias handling, unified cross-account search, how the pricing counts, and continuity across every provider your mailboxes live on. Score each criterion in a real trial against your actual mailboxes rather than a demo inbox.

The trap is a tool that treats several accounts as one bucket. It technically connects them, then triages your personal Gmail with the same signature block, the same tone, the same rules and the same autonomy setting as your client-facing work account. On day one that is invisible; in week three it fires an auto-reply to your sister from your law-firm address.

So the evaluation is not "does it support multiple accounts?" - most do. It is "does it keep them separate the way you need them separate, and does the pricing agree with the shape of your setup?"

The six criteria that actually matter#

Feature pages will list two dozen bullets per tool. These are the six that predict whether it survives a real four-mailbox setup past the first month. Everything else is a preference you can live with.

The scoring template#

Score two finalists on the same six criteria in one week, with the same real mailboxes, or you are not scoring - you are reading marketing pages back to yourself. Each criterion gets 0 to 3, and there is one triple-weighted line at the end.

Weight the pricing line triple#

Five of the six criteria are feature checks. The sixth - how the pricing counts - decides whether you can afford the tool at your real setup, and a wrong answer here is the one that reopens the decision a year later.

For a single operator running four mailboxes, per-mailbox pricing is punishing: you are paying four times the ticket for one person's inbox. Per-seat pricing is friendlier. Per-message metering is a coin flip that lands on its edge - the months you need triage most are the months the bill spikes.

• Per-seat with a mailbox count included in the seat - a single operator adding accounts pays once.
• Per-seat with unlimited accounts - the model that scales best for anyone running three or more inboxes.
• Per-mailbox - straightforward at two accounts, expensive at five, and often the reason people underuse the tool.
• Per-AI-action metered - manageable if the allowance is published and generous, dangerous if it is not.

Worked example: Priya, four mailboxes#

Priya runs a small legal practice. Her setup: a Google Workspace address at the firm, a personal Gmail, an Outlook mailbox for a property she rents out, and an IMAP account on a domain she has held for fifteen years and used for consulting. She sends from six addresses - the four mailboxes plus two aliases on the firm domain.

She trials two tools for one week each, scoring the six criteria. The interesting rows are not the ones where both tools score three.

Tool A scores 8 out of 18 on the six criteria and is disqualified on provider coverage regardless of how good the Gmail experience is. Tool B scores 16 out of 18 - the losses are one alias's DKIM alignment and a credit-metered AI pool that Priya would have to watch in a busy month.

The interesting line is not "which tool won" - it is "what did the losing tool do that the winning tool did not?" Tool A's Gmail experience was noticeably faster and its keyboard model was better. If Priya only had the two Gmail accounts, Tool A would win. She does not, so it cannot.

Red flags to end the evaluation early#

• The autonomy level is one global switch. Four mailboxes need four settings, not one.
• The pricing page does not say the words "per account" or "per mailbox" anywhere. It always means one of the two, and the vendor is hoping you find out on the invoice.
• Send-as goes through a proxy sending domain. Recipients see the correct From but DKIM aligns to the tool's domain, not yours, and your carefully-tuned deliverability regresses.
• The unified inbox is a marketing phrase for a folder list. If you have to click each account to see its threads, the tool has not unified anything.
• Outlook or IMAP is "coming soon" and the roadmap has been unchanged for six months. Coming soon in email tooling means never; ship dates are the least stretchy part of the calendar.
• The tool only connects one Google account per browser session because it does not support Google's multi-login pattern. Your two Gmail accounts will fight each other daily.
• Aliases are "supported" but each alias counts as a separate account in the pricing. Read that sentence twice - it is common, and it turns a four-mailbox setup into an eight-account bill.

How the pricing shapes actually work#

Four packaging shapes are worth naming plainly, because the difference between them is thousands of dollars a year at a five-mailbox setup and none of them is described the same way twice on any two vendor pages.

None of the four is wrong; they just fit different setups. Before scoring anything, decide which of the four your setup wants, then filter tools whose packaging shape does not match. This one filter cuts most shortlists in half in ten minutes.

Verify the current numbers against the vendor's own pricing page the week you evaluate. Prices in this category change three or four times a year, and a plan tier that made sense in March may not exist in November.

What we would pick, and where we lose#

We build AI Emaily, so this is our vendor's answer to the six criteria, scored against a real four-mailbox setup like Priya's. Per the plans on our pricing page as of August 2026: Starter connects two Gmail or Outlook accounts, Pro connects up to ten accounts across every provider, and Autopilot and Team are unlimited. It is per seat, and mailboxes are included in the seat - not billed separately.

On per-account autonomy, we have an explicit per-account Manual / Copilot / Autopilot setting, with rules scoped per account. On per-identity voice, we run a Personal Context you write plus client profiles you set - a distinct voice per address, without inferring anything from your past messages. On unified cross-account search, one search covers every connected mailbox, threading preserved. On provider coverage, Gmail, Outlook and Microsoft 365, iCloud, Fastmail, Proton and standard IMAP all connect natively without a relay.

The line we lose points on is send-as and aliases. We handle send-as on Gmail through Google's native mechanism, and on Outlook through the provider's shared-mailbox model, but on the trickier setups - IMAP with a smart-host relay, or a fourth-level alias on a domain whose DKIM policy is strict - you should test the raw headers in your recipient's inbox before scoring us 3. On the specific case of running many shared inboxes with granular per-address routing across a team, Missive has built that pattern longer than we have and it shows. If your setup is five shared inboxes across departments rather than four mailboxes for one operator, they are the better fit.

So the honest recommendation reads: if you are one person running two to ten mailboxes across Gmail, Outlook and IMAP and you want the AI behaviour separated per account, AI Emaily is what we built the tool for and the trial is at /pricing. If your setup is a team of ten sharing a handful of departmental inboxes, look at Missive first. If you live entirely inside Gmail and the other three mailboxes are hypothetical, a Gmail-native assistant will be faster on your one account than a multi-provider client can be. All three of those statements are true at the same time, and the choice follows from which one describes you.

One placement, one bridge#

The reason we lead with the scoring template and not the product is that the reader who applies the six criteria to any two tools will make a good decision even if the answer is not us. That is worth writing down because most posts on this query do not.

If our shape does describe your setup, the two links worth having open in another tab are /features/ai-email-assistant, which is what the AI actually does across the connected accounts, and /docs/unified-inbox, which is how the cross-account view is put together. Both are also on this post's related-docs list at the top.