Normally an email address has to exist before it can receive mail. With a catch-all it is different: the domain accepts everything addressed to it — including addresses that did not exist beforehand.
How it works technically
During delivery the sending server asks: "Do you accept mail for anything@example.com?" A normal server looks up its user list and rejects if the address is unknown.
A catch-all skips that step. It always answers yes and drops the message into a collecting mailbox — or, as in our case, into processing that creates the address on the spot and assigns the message to it.
That is why with a service like ours you can simply invent an address. It does not need registering; it comes into existence the moment the first message for it arrives.
What it is good for
- A separate address per provider. If you own a domain you can use
shop-xy@my-domain.comwithout setting anything up first. If advertising later arrives through it, you know immediately who passed the address on. - No mail lost to typos. If someone writes
inof@instead ofinfo@, the message still arrives. - Temporary addresses without registration. Exactly the principle this service is built on.
The downside
Spam with no brake
The biggest drawback: a catch-all can no longer reject mail on the grounds that the address does not exist. For normal mailboxes that rejection is the first and cheapest line of defence. Anyone guessing addresses — info@, contact@, max@ — always hits with a catch-all.
A giveaway for attackers
Because the server confirms every address, it indirectly reveals that it runs a catch-all. Providers use exactly this to detect and reject temporary address services — we covered that in a separate post.
Bounces and reputation
Anyone sending to a catch-all domain never gets an error, even if the address is nonsense. For senders trying to keep their lists clean that is a problem: the usual feedback is missing. Some sending services avoid catch-all domains for that reason.
Sorting
If everything lands in one collecting mailbox, somebody has to sort it. Here the application does that by assigning each message to an alias based on the recipient address — which is why your mailbox only shows what was addressed to exactly your address.
The alternative: defined aliases
Instead of a catch-all you can create a manageable number of real aliases pointing at one mailbox. That is slightly more administration but has a decisive advantage: unknown addresses get rejected, so the first filtering stage works again.
For a personal domain a catch-all is convenient. For a domain receiving business mail, defined aliases are usually the better choice.
What that means here
For us the catch-all is part of the concept: you should be able to invent an address without registering. The price is that we cannot pre-filter incoming mail by address. So we rely on other means — blocked alias names, fixed retention periods and review of outgoing messages. What that achieves and where the limits are is in our post on preventing abuse.