Junk stays quiet.
Your mail server already sorts out most spam. Postfach follows what it decides, never announces it, and adds rules of its own for what still gets through: mail with an emoji in the subject, mail in an alphabet none of your correspondents use, and rules you make from a message in Junk, out of its rarest words. The senders you trust stay out of all of it.

Your server's filter comes first.
Postfach shows each account's Junk folder as your server keeps it. A new message is announced only if it is still in the inbox, and still unread, a few seconds after it arrived. So spam your server moves to Junk as it is delivered never lights up your phone.
- Junk is not counted in the unread number on the app icon
- A search across all mailboxes leaves Junk out
- Addresses in Junk are never suggested when you write
- Junk rows are drawn in ochre, so a message that is there is recognised at a glance

Rules for what gets through.
Two are switches, turned on for each account in Settings › Junk. Emoji in the subject moves new mail like “🎉 You have won” or “📦 Your parcel is waiting” to Junk. Alphabets moves new mail whose subject is written mostly in one you tick: Chinese, Japanese kana, Korean, Cyrillic, Greek, Arabic, Hebrew, Thai, Devanagari, or Latin.
The rules act on new messages as they arrive in the inbox, and move them to Junk on the server too, so every other mail app sees the same. Mail already in your inbox stays where it is.
The third kind you make yourself: junk rules, for the junk your server lets through. On a message in Junk, choose Make a Junk Rule…: Postfach ticks the whole subject, which is saved as a rule of its own, proposes the message's rarest words, rare as measured in your own mail and never a word of your everyday mail, and shows what the rule would catch while you tick the words: a line above the form counts the mail you kept that it would move, and the matches in Junk and Trash; on the Mac and the iPad a panel beside the form lists them, each message with the words it holds, so the word to untick is plain. New mail that matches goes straight to Junk, without a notification. A message a rule moved says which one, and Not Junk on it offers to change the rule. The rules are in Settings › Junk Rules, where one switch can offer a rule each time you mark a message as junk, and another leaves the subject unticked.
- A message you mark as Not Junk is never moved again
- Tick only alphabets none of your correspondents write in: mail from anyone who does is moved as well
- Mail from your own accounts in Postfach is never moved, so templates you send to yourself arrive in the inbox
- For Japanese, tick Chinese and Japanese kana together
- A junk rule never moves mail from anyone you have written to, nor from a trusted sender your server confirmed
- When you save a junk rule, the matching mail in your inbox can move to Junk at once, and you untick the messages that should stay

Trusted senders stay out of Junk.
Postfach Contacts is an address book of Postfach's own, for the people whose mail must not be caught. The people you write to are in it by themselves. A sender you mark as Not Junk joins them once your mail server confirms that the message really came from them; you can also trust a sender from a message's menu, or add an address yourself.
Trust counts only for a message whose sender your server confirmed, so a forged From line gets nothing. For a trusted sender, the junk rules never move their mail, mail your server's filter put in Junk comes back to the inbox, and their remote images load, in every account. The last two are switches in the book, on unless you turn them off.
- On the Mac in the Window menu; on the iPhone and the iPad, Contacts in the mailboxes
- Rename an entry, stop trusting it, or remove it
- Sorted by name, or grouped by the account each came from
- Trusted people come first among the suggestions when you write
- A settings export carries the book only if you choose to

The same rules on every device.
Junk rules and trusted senders are each device's own: nothing of them is kept with us, because nothing is. So Postfach sends them through your own mail. In Settings › Junk Rules, Send Junk Rules by Email… mails the rules, and the senders you trust or do not, from one of your accounts to another. On your other device the message shows a banner, and Import… replaces what that device has, after a summary of what is added, removed, and changed.
And where two devices still differ, they no longer argue: a device moves a message to Junk once, and brings a trusted sender's message out once. What another device, or you, did after that is left alone.
Your templates, and your whole setup, get across too. More about your devices →
- Only a message from one of your own accounts is offered for import
- What an import replaces is kept: Restore Junk Rules… brings it back
- Rules for an account the other device does not have are left out, and its own rules for an account the sender lacks stay
One move either way, one tap to empty.
Mark a message as Junk and it goes to the Junk folder of its account; Not Junk sends it back to the inbox. Delete Junk Mail empties the folder after asking once, and deleting more than three messages anywhere asks first too.
- Swipe from the right on the iPhone and the iPad for Junk, or Not Junk inside Junk
- On the Mac: ⇧⌘J for Junk and for Not Junk, and Folder › Delete Junk Mail… to empty the folder
- On the iPhone, Delete Junk Mail sits above the list while you are in Junk

And the things spam cannot do.
Know you opened it
In Junk, images from a sender's server stay blocked until you ask, even for an account that loads them always, so opening a message there tells nobody that you did. On the Mac a message there is not even loaded until you click Load Junk Message. Scripts in mail never run.
Get into your conversations
Conversations are gathered from every folder of the account except Junk and Trash, so a reply-shaped spam message does not attach itself to a real thread.
Train a filter somewhere else
The rules run on your device, with your settings. Nothing about your mail, spam or not, is sent to us or anyone else to learn from.