My filter isn't working. How can I test it?

What I really need is the ability to obtain the result of a pipe command so that I can filter externally and redirect internally. Is this possible?

I received a message with a Subject: line that contained a non-printing character (a carriage return). This messed up my filter file. Is there a way to get round it?

I want to search for $ in the subject line, but I can't seem to get the syntax.

My problem is that Exim replaces $local_part with an empty string in the system filtering. What's wrong or what did I miss?

Using $recipients in a system filter gives me another problem: how can I do a string lookup if $recipients is a list of addresses?

What are the main differences between using an Exim filter and using procmail?

How can I allow the use of relative paths in users' filter files when the directories concerned are not available from the password data?

How can I set up a filter file to detect and block virus attachments?

Is it possible to write code for scanning messages in Python?

Whenever my system filter uses a mail command to send a message, I get the error User 0 set for address_reply transport is on the never_users list. What does this mean?

I'm trying to reference the Envelope-To: header in my filter, but $h_envelope-to: is always empty.

I want my system filter to freeze all mails greater than 500K in size, but to exclude those to a specific domain. However, I don't seem to be able to use $domain in a system filter.

When I try to send to two addresses I get an error in the filter file malformed address: , e@fgh.com may not follow a@bcd.com. What is going on?