I encountered the following problem and decided to post my work-around solution here in case anyone else needs it. (The redundant spellings in the subject should help people find the message using different search keywords.)
BACKGROUND:
I previously used a catch-all alias with extensive content filtering to avoid spam; however, it became difficult to manage this
system and decided to switch to a single (new) email address (that I will change again when I begin to receive too much spam). However, in case I forgot to tell someone my new address, I wanted to change the catchall to tell a sender how to reach me at the new address.
I changed the catch-all alias to forward messages to a special account called "respond". I set up an auto-responder on the special account, telling a sender that my email address has changed and they must fill out a form on my website (a la SpamArrest). I also set up a content filter on the special account to bounce every message (any message larger than 0K).
PROBLEM:
If a user sends a message to a non-existing address at my domain, the catch-all alias forwards the message to the special account. However, the special account neither sends the auto-response nor bounces the message. I was able to determine that the special account receives the message by temporarily removing the bounce filter, which allowed test messages to appear in the Inbox.
Ironically, if a user sends a message directly to the catch-all alias, the special account behaves as expected: it sends the auto-response and also bounces the message! The failure only takes place when the catch-all is used to handle a non-existent address!
SOLUTION:
I set up a second special account named "filter" and set up a content filter there to forward all messages to the "respond" account. Then, I changed the catch-all alias to redirect messages to the "filter" account. So, any message sent to a non-existent address is caught by "catchall", forwarded first to "filter" and then on to "respond". When I tested this arrangement from four different domains (all on different servers), the sending account received both the auto-response and bounce EVERY TIME!
Actually, I set up two content filters on the "filter" account: the first forwards messages containing the word "received" in the header to the "respond" account; the second deletes any remaining message larger than 0K. In my experience, any message without a "received" header is always spam or a system error message, and therefore need not be handled.
NOTE: I am unlikely to monitor this forum for future questions, but I hope this information helps.