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#### 8.2.3 What nnmairix does

The back end `nnmairix` enables you to call mairix from within Gnus, either to query mairix with a search term or to update the database. While visiting a message in the summary buffer, you can use several pre-defined shortcuts for calling mairix, e.g. to quickly search for all mails from the sender of the current message or to display the whole thread associated with the message, even if the mails are in different folders.

Additionally, you can create permanent `nnmairix` groups which are bound to certain mairix searches. This way, you can easily create a group containing mails from a certain sender, with a certain subject line or even for one specific thread based on the Message-ID. If you check for new mail in these folders (e.g. by pressing `g` or `M-g`), they automatically update themselves by calling mairix.

You might ask why you need `nnmairix` at all, since mairix already creates the group, populates it with links to the mails so that you can then access it with Gnus, right? Well, this might work, but often does not—at least not without problems. Most probably you will get strange article counts, and sometimes you might see mails which Gnus claims have already been canceled and are inaccessible. This is due to the fact that Gnus isn't really amused when things are happening behind its back. Another problem can be the mail back end itself, e.g. if you use mairix with an IMAP server (I had Dovecot complaining about corrupt index files when mairix changed the contents of the search group). Using `nnmairix` should circumvent these problems.

`nnmairix` is not really a mail back end—it's actually more like a wrapper, sitting between a “real” mail back end where mairix stores the searches and the Gnus front end. You can choose between three different mail back ends for the mairix folders: `nnml`, `nnmaildir` or `nnimap`. `nnmairix` will call the mairix binary so that the search results are stored in folders named `zz_mairix-<NAME>-<NUMBER>` on this mail back end, but it will present these folders in the Gnus front end only with `<NAME>`. You can use an existing mail back end where you already store your mail, but if you're uncomfortable with `nnmairix` creating new mail groups alongside your other mail, you can also create e.g. a new `nnmaildir` or `nnml` server exclusively for mairix, but then make sure those servers do not accidentally receive your new mail (see nnmairix caveats). A special case exists if you want to use mairix remotely on an IMAP server with `nnimap`—here the mairix folders and your other mail must be on the same `nnimap` back end.