Thanks. I did wonder if you might have been thinking of Pegasus, but I use Thunderbird so am not familiar with it. I've been doing it at client level in Thunderbird, but my android device doesn't seem to have the facility and I was hoping to do it at server level. I can see why, on reflection, that it's not really a server function. Anyway, thanks for your help, as I now know that what I was trying to do is impossible, so can stop trying.

I would like to filter all mail from a particular sender so that it goes into a folder, marked as read, rather than my Inbox. This seems an obvious thing to want to do, but I can't see 'move to folder' listed as an action under Global Rules. Please can anyone help?

Since you want to filter all incoming mail it would be better to create the rule as a new mail filtering rule when folder is opened.  All incoming mail automatically get processed through these filter rules.

To perform two actions (mark as read and move) I find it most logical to branch to a label something like this:

Be sure to end the rules in the label with an "Exit this rule set" rule to insure processing is stopped at the end of each label.

Thank you, Brian, that gave me something to work on. I have realised I only want to filter all mail to one user, not all users. I've created an Alias for the user, and a .rul file. Based on previous successful .rul files I have the first line

 If "From" field contains "targetdomain.com", then goto Label1

This is not triggering, as the line below is being executed irrespective of the from field.

I am also struggling to find the correct syntax for the target folder name. I have tried

Always move to folder "Username/Foldername"

but this does not work (I also tried \ rather than /)

Further advice would be appreciated!

My bad for responding the way I did.  I responded as appropriate for Pegasus Mail missing the fact that this is the Mercury forum.  Please accept my apology for that.

As for Mercury, there isn't a way to set the "has been read" status nor filter directly into a folder from Mercury.  Those would need to be done at the client level.  The best you can do in Mercury is to create a filter that detects the sender and then set the appropriate action, which I think in your case is to use the "move to another user" action.  This gets it into the appropriate users mailbox where the filters of the email client can handle manipulation into a specific folder.

In Mercury, the global rules are in a file named RULES.MER.  The rule would look like:

If header "F" contains "targetdomain.com" Move "localusername"

I'm not a fan a editing the rules file directly but I understand that plenty of folks do.  I prefer to use Mercury's rule editor.