Non-existent aliases should default to error code 550 (hard bounce)

[junxit]

I noticed today that if someone emails [email protected], it does not bounce (goes to the blackhole).

This is less than ideal, since I as the owner/admin of example.com cannot always foretell what aliases people will use that I have not created yet.

As a workaround, I created [email protected] which is inactive and set to return error 550, then I created a catch-all *@example.com that forwards everything to [email protected], and that works fine (as I expect it to).

Also, if I have a valid email alias [email protected] that forwards to [email protected], it still forwards correctly (no bouce) despite the catch-all that I set up.

Question posted by this chat thread:

1. Should the default behavior for non-existent aliases be to return SMTP error 550 (hard bounce)?
2. Should this behavior be made configurable at the domain level?
3. Alternatively, the catch-all (*) alias can be modified to allow it being added as disabled (today, disabling the catch-all forces you to remove it altogether), to achieve the behavior I get with my above workaround, without having to create a separate [email protected] that is disabled

Thoughts?

[shaunwarman]

Hey @TheJade

You could (and may already have based on the above) setup a catch all alias and then set the bounce reject rules appropriately. You're right it is a 250 quiet bounce (blackhole) by default today. But you could set a soft or hard reject.

[junxit]

Unfortunately, this does not work. The settings you shared a screenshot for are only active if the Active checkbox is unchecked, and if you uncheck the box, you get this upon attempting to save the settings:

This is why I suggested # 3 in my original post.

[shaunwarman]

Good call out. After some discussion we can default to 550 hard bounce. Just wanted to see if any issues around spam or security here. After that we can take a look at some extra configurability options based on your original message.

[junxit]

Good call out. After some discussion we can default to 550 hard bounce. Just wanted to see if any issues around spam or security here. After that we can take a look at some extra configurability options based on your original message.

Agreed that someone can use the 550 or lack thereof to figure out if an alias exists or not. Making it configurable would likely be best.