Comparison
Kerna vs MailMaestro
Both run in Gmail and Outlook, and both sort, summarise and draft. The difference is who names the categories: MailMaestro applies its own set — To Respond, FYI, Marketing — and Kerna sorts into the set your team writes, up to six of them, or one of 20 built for an industry.
What Kerna brings to the day
- Categories you write, not a label set somebody else chose.
- Named fields out of a PDF, not a summary of it.
- Zero retention on message content from the free tier up, not only on an enterprise contract.
Every MailMaestro figure below was read on maestrolabs.com and carries the date it was checked. Last reviewed .
Who each is for
Two different jobs
Kerna is for the operational inbox
The inbox where quotes, spec changes, invoices and complaints arrive from outside the company, and where somebody has to work out what each message needs before anything happens. Drafting is part of that, not the point of it.
MailMaestro is for an inbox labelled and drafted for you
Compose, reply, improve, templates and shared team tones, alongside automatic labels, a priority view and summaries of threads and attachments. The sorting and the writing are both done for you, from its own set of labels.
Overlap
What both of them genuinely do
Worth being clear about, because the differences below only mean something once the overlap is named.
- Running inside both Gmail and Outlook rather than asking you to move to a new client.
- Summarising a thread you have not read.
- Drafting, replying and improving text in the compose window.
- A free tier, so neither has to be bought before it is tried.
- CASA Tier 2 verification, which both have completed.
Differences
Where they actually diverge
Who defines the categories
Kerna
Five built-in categories — Urgent, Respond, Invoice, Waiting, Notification — replaceable with a taxonomy of your own of up to six, or one of 20 built for specific industries.
MailMaestro
Automatic labels applied to incoming mail, from a set the product defines — To Respond, FYI, Marketing — with automatic prioritisation and a priority view on top. The page describes no categories the customer writes.
Which plan the strongest retention terms are on
Kerna
Zero retention of message content is architectural rather than a setting, and applies on every plan including the free one. Account, subscription and usage records are kept, on the schedule set out in the Privacy Policy.
MailMaestro
The security page states retention is "only as long as needed to provide the service", with zero-day retention available to enterprise customers rather than by default. A five-person team on the paid tier does not get it.
What reaches the model
Kerna
Personal data is redacted from the message inside Kerna’s own processing, on every request, before any content is transmitted to the inference provider.
MailMaestro
The security page describes nothing being removed from message content before it reaches the model.
How it reaches Gmail
Kerna
A Google Workspace Marketplace add-on, which is why it runs in the Gmail mobile app as well as the browser.
MailMaestro
A Chrome Web Store extension rather than a Workspace add-on, so it does not run in the Gmail mobile app. The Outlook side is a marketplace add-in.
What comes out of an attachment
Kerna
Structured extraction across PDF, DOC and XLS with 100 field presets — 20 industries by 5 document types — exporting to Excel, Word or CSV in Outlook, and Sheets or Docs in Gmail.
MailMaestro
Summarising attachments with AI, on the Professional and Team tier. A summary of the document, rather than named fields lifted out of it into a file you can open.
Cost
What each one actually costs
Read from each vendor’s own pricing page, with the date. If a figure is not verified, it is not stated.
Kerna
- Entry price
- Standard: EUR 12 per month. Pro: EUR 22 per month. Free Starter available.
- Read on the vendor’s own page · checked 2026-08-22
- Five seats
- Business: EUR 69 per month for up to five users sharing 7,500,000 tokens.
- Read on the vendor’s own page · checked 2026-08-22
- Free tier
- Yes. Starter includes all functions within its token allowance.
- Read on the vendor’s own page · checked 2026-08-22
MailMaestro
- Entry price
- Professional/Team: USD 15/user/month or USD 144/user/year, equivalent to USD 12/month.
- Read on the vendor’s own page · checked 2026-08-22
- Five seats
- USD 75/month or USD 720/year for five Professional/Team users; annual equivalent USD 60/month.
- Read on the vendor’s own page · checked 2026-08-22
- Free tier
- Yes. After a 14-day trial, Free permits three compose, reply or improve requests per week.
- Read on the vendor’s own page · checked 2026-08-22
Five seats is EUR 69 a month on Business against USD 75 on Professional/Team, in each vendor’s own currency. The prices are in the same region; what each includes is not.
Data handling
Where content goes on each side
Both vendors publish a serious position. They differ on when you get the strongest version of it.
Kerna
- Processing
- The application runs on Google Cloud Run in Belgium, with Firestore in Poland. Kerna masks detected personal data before model processing and has a zero data retention agreement with OpenAI Ireland Limited. Account and usage data have separate retention rules. The model-processing location must be established from the applicable configuration and terms, not the contracting entity’s address.
- Read on the vendor’s own page · checked 2026-08-22
MailMaestro
- Processing
- Maestro Labs publishes SOC 2 Type II, CASA Tier 2 and Microsoft Attestation information. It states that data is not used to train AI models and is encrypted in transit and at rest. Retention is limited to service needs; zero-day retention is available to Enterprise customers.
- Read on the vendor’s own page · checked 2026-09-05
Kerna’s full position, clause by clause, is on the trust page.
When Kerna is the better fit
- Work arrives from outside the company and has to be sorted before it can be actioned.
- The categories that matter are yours — Quote requested, Spec change, Chasing payment — not generic labels.
- You want to put a real morning of mail through it before anyone buys anything, rather than three requests a week.
- Somebody on the team works Gmail on a phone.
- You need named fields out of the PDF, not a summary of it.
Where MailMaestro already fits
- The bottleneck is writing speed rather than working out what arrived. That is what MailMaestro is built around, and shared team tones are part of it.
- You want meeting notes and document drafting from the same vendor on one subscription. Kerna does email and nothing else.
Try it on one morning’s inbox
The free tier costs nothing and installs in minutes. A single morning of real mail settles this faster than any comparison table.
Deployment
Getting it in front of a team
Time to value
Kerna installs from the Google Workspace Marketplace or AppSource, or an administrator deploys it for the whole organisation. There is a free tier at €0, so getting it in front of someone costs nothing. What each tier includes is on the pricing page.
What it needs
For Outlook: a Microsoft-hosted mailbox. Mailboxes on POP, IMAP or on-premises Exchange are not supported. Gmail has no such restriction.
The gap worth knowing first
What Kerna does not have: configurable company single sign-on (you sign in with your Microsoft or Google account, but there is no SAML or OIDC connection to your own identity provider), SCIM, SOC 2, and Outlook mobile — though the Gmail add-on does work in the Gmail mobile app. Stated here rather than left to be discovered, because a requirement is easier to check now than after an install.
Other comparisons
Comparing something else
Same method on each: figures read from the vendor’s own pages, dated, and the parts where they win stated plainly.
Still working out what to compare on? Seven questions to ask any vendor.
Try it against one morning’s inbox
Kerna’s Starter tier is €0, includes every feature, and carries a trial token allowance to run them on. Install it in Gmail or Outlook, put one morning’s real mail through it, and see whether the categories that come back are the ones you would have written.
MailMaestro is a trademark of Maestro Labs PTE. LTD. Gmail and Google Workspace are trademarks of Google LLC; Outlook and Microsoft 365 are trademarks of the Microsoft group of companies. Kerna is not affiliated with or endorsed by any of them. Comparative statements reflect each vendor’s own published documentation on the date shown.