The first question is never a technical one
Nobody asks how to connect a mailbox first. They ask who is going to read their email. The question is a healthy one, and a product that dodges it does not deserve an answer.
A work mailbox holds the best knowledge a company has, the commitments made, the deadlines negotiated, the reasons behind a refusal. It also holds the doctor's appointment, the letter from the building manager and a conversation with a former colleague. Both land in the same place, and that is the whole difficulty.
Business mail, and business mail only
A mailbox is the most delicate source a company can connect. Here is the boundary, unrounded.
Sorting private from business is a judgement, and judgement errs. This one is tuned to err in a single direction, exclusion: a business message wrongly discarded costs context, a private message wrongly taken in would be a fault.
The sorting happens before the writing, not after
The order of operations is the only thing that matters here. Every message is examined before anything at all is written into your Kastel. What is judged private, or mixed, is not written and then deleted later; it is never written.
The sorting leans on explicit rules first, then on a model you connect with your own keys. Kastel never resells inference and takes no margin on it: the sorting of your mail runs on the account of the AI provider you chose, and you can change provider.
If no sorting model is configured, the connector refuses to work. It does not take the mailbox in “for now”. Refusal is the default behaviour, and taking mail in requires an explicit configuration.
Your mailbox is connected by you
The Gmail authorisation is given per person, not per company. Each employee goes through Google's own consent screen for their own mailbox, and sees exactly what is being requested, a read permission and nothing else.
The connection also compares the Google account address with the person being connected. If that address belongs to someone else your organisation already knows, it refuses: nobody connects a colleague's mailbox under their own name, not even through a typing mistake. An address your organisation does not know yet does not block the connection, because an administrator may be adding that person in the same change.
The questions we get asked about this connector
Will my manager be able to read my email through an AI?
They will be able to reach the business mail from your mailbox if they belong to the same department as you, because what is kept is filed under that department. They will not reach your private mail, which was never written down. And someone from another department reaches neither. We would rather write that than let you find it out.
What about a personal message sent to my work address?
It is discarded before anything is written, like any message judged private. A message mixing both registers is discarded too: in case of doubt, the connector excludes rather than includes.
Can an AI send mail on my behalf?
No, not through this connector. The only permission requested from Google is a read permission. There is no write path towards your mailbox, so the question is not settled by a setting, it is closed at the permission level.
What happens if I disconnect my mailbox?
The access key is deleted and not one more line comes in. The mail already read stays in place, with the same read permissions as before, until an administrator decides to erase it: detaching a source and erasing its content are two separate gestures, deliberately so. You can also export the whole of your Kastel at any time, without asking us. Kastel is not exempt from its own rule: full export at any time, free self-hosting for life.
What this connector does not do
It does not read ten years of archives. The connection reaches back a window of a few months, ninety days by default, and whoever deploys it can widen that. That window is a design choice rather than a technical limit. We prefer freshness to archaeology, because a message from 2019 describes a process that no longer exists.
The private-mail sorting is not perfect and we will not pretend otherwise. It sometimes discards a business message, typically when a client writes in a personal tone. That is the direction we would rather be wrong in.
Reading is the only verb. Kastel sends nothing, replies to nobody, archives and deletes no message.
And deleting a message in Gmail does not remove it from your Kastel. On the following pass it is marked there as gone at the source, and it stays reachable by those who were already entitled to it until an administrator erases it. That is a deliberate choice: an answer already given has to remain verifiable. Erasure itself is an explicit gesture, and it reaches down to the derived traces.
Install the free core and judge it on your own mailbox.
Kastel's core is free to self-host, on your own machines, with every connector. The best way to know what an AI reads of your mail is to watch it happen on your own hardware, with your own keys.
Read the connection guide
