Before I post my primary question, I must ask about some general issue about the "search" feature on this site (just because I failed to find the topic that interested me). As I cannot find any help on this:

0) Does this work at all? (I tried to find topics with some common words, like "attachment" and I couldn't see any reports on the search result, neither the forum topics seemed to be filtered)

1) Does this search based on titles only or does it look through the post content also?

2) Does this search using by default OR or AND operators between words (ie. finds any occurrence of any of the words or only the exact phrase)?

3) Can the logical operators of any kind be used (like quotation marks, -, .NOT. etc.?

Sorry if I've overlooked something,
crayfish

The search function of this forum is very odd. I can't answer your questions about operators but I can tell you that the search function works, and that it searches both topics and content.

Open the forum category that you want to search the use the magnifying glass at the top to enter a search term. The subsequent results will include a pane containing more search options. There is a rudimentary discussion about it here (ignore my first irrelevant response):
https://community.pmail.com/index.php?u=/topic/12161/search-previous-messages/post-57173#post-57173

Oh, yes, only now I noticed the magnifying glass on the very top, near the "Report links" and login buttons, thanks! And as far as I see (from the linked discussion) I'm not the first to miss it... ;-)

It seems that more visible is that, which appears when you scroll down the topic list. So, although the "upper" is what I was looking for, as a 'spin-off' I'd like to know, what is this "lower search window" for? (I mean when you view the topics' titles, not this within the topic, the function of which is described at the discussion you linked).

This appears, analogically to that of a within-discussion search, only after you scroll lower than the first 1-2 topic titles:

I cannot see any action if I write something into this and press enter or click the magn. glass on the right (only a mouseover "Advanced search" appears, but to no effect). What could I have overlooked here?...

Greetings,
crayfish

You haven't overlooked anything. That search field doesn't work for me either when attempted while viewing the list of discussion topics in a category. Oddly, when viewing a discussion, that search field works to search that discussion.

OK, so I guess we can close the topic (there's no such formal feature in this forum, as far as I can see) with an appeal to the forum's IT supervisors to make something with this...

Thanks for the feedback, Brian!