Source Account:

Filters messages according the server you got them from. This is most useful if you use multiple POP mail accounts.

Pipe to Program:

Evolution can use an external command to process a message, then process it based on the return value. Commands used in this way must return an integer. This is most commonly used to add an external junk mail filter.

Junk Test:

Filters based on the results of the junk mail test.

Match All:

Applies an action always to any message, without further conditions. This could be useful at the end of the list of message filters to cover those emails that did not match any conditions for the preceding filters in the list.