Do you mean that you want all mail to be copied to another account, which can then be polled? If so, use the Configuration>Filtering Rules>Edit Global Rules and setup a rule to copy all incoming mail using the 'Always triggers' rule. Set it up to copy all incoming mail to an account of your choice.

Does the existing Postmaster account act as a catch-all or is there another way to create one?

Cheers. 

Not sure what you are asking since I'm not sure how yuo are receiving your mail.

1.    If you are receiving mail from a POP3 "domain" account via MercuryD then you set the "default" user to get any mail where there is no matching local user or alias.   

2.    If you are receiving your mail via MercuryS then you can set a domain account to catch all mail for a specific domain and put it into a user account.  There is no way to set a default user with MercuryS to get mail where there is no matching user or alias.

Just for completeness: If you are using MercuryS to receive mail there is an option to accept mail for invalid local addresses. From Mercury help:

Accept mail for invalid local addresses  In regular use, MercuryS will refuse to accept any message that appears to be addressed to a local user who does not exist. This refusal can result in the sender getting unhelpful mail messages from their mail program. If you check this control, Mercury will accept the message and the Mercury core module will later reject it and send it back to the sender, but in a more clearly-explained form. Mercury will also refer a copy to the postmaster, who can then correct any addressing error and pass it on to the proper recipient.

/Rolf 

Actually I do not recommend doing this since it causes a lot of backscatter when you receive mail from spammers using a dictionary attack.  It also causes a lot of problems to the person in the RFC 2822 message Sender: and/or Reply to field since this is used in bouncing the message rather than bouncing it back to the sending server.

I run a Forum and offer members an email account on my domain. I use a script that polls a catchall account, then it distributes the email to the aliases they set up within the forum.

It worked fine using  hMail but it uses too many resources for me so I am trying out Mercury, but it doesnt seem to have a catch all account to facilitate what I need.

Cheers 

You can setup a domain account on Mercury/32 fairly easy.  In the domains section you setup a domain pointing to a user using the DM-<username> and the domain.  For example if all mail for anyuser@your.domain.com is to go to a domain account yuo would create a user called domain and then set DM=domain : your.domain.com

All of the mail goes into the "DOMAIN" user new mail directory as  RFC 2822  message bodies.  It's not that difficult to create a script to forward the mail based X-Envelope-To: header that contains the original RCPT TO: address.

What you cannot do though is have the same domain in the domains section twice.

If this is you primary domain you can setup aliases for all of the addresses that stay on the local server and the others go to the domain accout.

I'm not at all sure I know exactly what you are trying to do though since I use maling lists to do all this sort of communication.