How to Choose an AI Email-Reply Assistant: Drafting Help vs Autopilot

An AI email assistant is worth paying for only when it saves you real time, not when it just makes your inbox feel managed. Email is where a “smart” feature is easy — and potentially expensive — to get wrong: a mis-toned reply to a client or a fully automated message that sounds like a bot can cost you more than the subscription ever did. Before you buy anything, decide whether you need help drafting, a faster review-before-send workflow, or automation for a narrow set of routine replies.

Control falls on three levels: AI drafts that you review and send, generated replies that need only a quick confirmation, and rules that can send without review. A common costly mistake is buying more automation than the risk of your messages can justify. Figure out how much of your email truly needs your judgment, and the price point mostly resolves itself.

The three real options

Vendors move tiers and prices often, so confirm the current plan and billing cycle before you commit.

Draft-first assistants (Superhuman Mail, Shortwave). These live next to your inbox and propose a reply you approve or edit before it sends. Superhuman Mail’s standalone plans list Starter at $30 month-to-month or $300 a year; Business, which adds Auto Drafts and Ask AI, is $40 month-to-month or $396 a year. Superhuman also offers Mail inside a Business suite, so check which checkout and bundle your account is offered. Shortwave has a free plan that includes its AI executive assistant, while advanced AI search and writing personalization are paid features; its public documentation does not promise a fixed monthly number of free AI replies. The trade-off is straightforward: you keep control of tone, but you still read every reply, so your saved time is the writing, not the judgment. This fits client-facing mail when the replies are formulaic enough that a first draft saves effort.

Review-before-send and conditional automation (Missive and inbox rules). Some systems stop at a draft; others can run rules on incoming messages and prepare or send a response under conditions you define. Missive is a shared inbox for teams. Its Productive and Business plans are listed at $24 and $36 per user per month when billed yearly. Missive’s AI documentation says AI requires one of those plans plus an API key from OpenAI, Anthropic, or Google, with provider usage billed separately. The catch is trust: a prepared reply can still contain a tone or fact error. Test auto-send only for short, low-stakes, high-volume messages such as booking confirmations or routine follow-ups, and keep client-sensitive mail behind a human review step.

Built-ins and existing-plan features (Gmail, Outlook). Start with whatever your current account already includes, but do not assume every AI drafting feature is free. Google says Gmail’s “Help me write” is available globally through eligible Workspace or Google AI plans and, for personal Google Accounts, only in the United States. It can draw on other emails and Drive files and match your tone, so capability depends on account access rather than a blanket lack of context. In the United States, Outlook Copilot is included in paid plans such as Microsoft 365 Personal, listed at $9.99 a month or $99.99 a year, rather than being a generic free Outlook feature. For a freelancer or small team with light email volume, features already included in an existing plan are the baseline against which a separate subscription should justify itself.

Who should pick which

Match the tool to the stakes, not to the brand:

• Client-facing and quote-worthy email: use draft-first. You want the writing speed, but a client, an editor, or a colleague might read your reply — keep a human in the loop because auto-send can create avoidable client risk.
• High-volume, low-stakes mail (support, bookings, confirmations): automation may be worth testing. If the downside of a wrong reply is limited and the volume is high, define narrow send rules and review the exceptions.
• A few short email conversations a day: first test the features already included in your account. For example, a separate $30 plan you barely use is worse value than no additional subscription, but Gmail and Outlook access varies by region and plan.
• A shared team inbox: pick a tool built for shared context, permissions, and assignments unless your existing setup explicitly supports those needs.

A test for whether it’s worth paying

Run this before subscribing. During a normal working week, record how many replies you send and the minutes from opening each thread to sending the reply. Then repeat the measurement with the assistant on similar messages, including review and editing time. Use your measured difference rather than assuming a 50% saving, and extend the test if a trial or sample does not cover enough of your usual client, support, and internal mail.

Then put a number on it. Use this formula: weekly replies × net minutes saved per reply × 4 weeks ÷ 60 × your hourly rate. Suppose you write thirty client-adjacent replies a week at two minutes each, and the measured assisted time is one minute. The tool saves 30 minutes a week, or 2 hours in a four-week month. At a $50 hourly rate, that time is worth $100 a month, so a $30 plan leaves $70 of time value before you account for errors or variable workload. If the assistant saves only 10 seconds per reply, the same formula gives about 20 minutes, or $16.67, a month; the plan misses break-even by $13.33. For this workload and rate, a $30 plan breaks even at 36 saved minutes a month: 9 minutes a week, or 18 seconds across each of 30 weekly replies. Set a larger safety margin only if you choose it for your own workload risk, and label it as your margin rather than a universal rule.

At the end of the trial, compare total net minutes saved with the subscription fee and note any unacceptable fact or tone errors. A low no-edit rate is not an automatic rejection if the edits are quick and the measured time value still clears the fee. Conversely, a high acceptance rate does not make auto-send safe for messages whose downside you cannot accept.

That’s the core of it: email assistants sell speed, and speed has a measurable threshold. Start with features your existing plan includes. Pay for drafting when your measured monthly time value exceeds the fee, and pay for automation only when the replies are low-stakes enough that a bad one does not create an unacceptable cost.