Gnus will read the mail spool when you activate a mail group. The mail file is first copied to your home directory. What happens after that depends on what format you want to store your mail in.
There are six different mail back ends in the standard Gnus, and more
back ends are available separately. The mail back end most people use
(because it is possibly the fastest) is
nnml (see Mail Spool).
|• Unix Mail Box||Using the (quite) standard Un*x mbox.|
|• Babyl||Babyl was used by older versions of Rmail.|
|• Mail Spool||Store your mail in a private spool?|
|• MH Spool||An mhspool-like back end.|
|• Maildir||Another one-file-per-message format.|
|• nnmaildir Group Parameters|
|• Article Identification|
|• NOV Data|
|• Article Marks|
|• Mail Folders||Having one file for each group.|
|• Comparing Mail Back Ends||An in-depth looks at pros and cons.|