# Courier Documentation

Please note that the online version of these manual pages reflect the installation directories used for development and testing. When you install Courier, the actual installation directory you use will be reflected in your manual pages.

## Manual pages

`cancelmsg(1)` `couriermlm(1)` `couriertls(1)` `courierlogger(1)` `dot-forward(1)` `lockmail(1)` `maildirkw(1)` `maildiracl(1)` `maildirmake(1)` `mailbot(1)` `maildrop(1)` `makedat(1)` `makemime(1)` `mimegpg(1)` `preline(1)` `reformail(1)` `reformime(1)` `sendmail(1)` `testmxlookup(1)` | `maildropex(5)` `maildropgdbm(5)` `maildropfilter(5)` `dot-courier(7)` `localmailfilter(7)` `maildirquota(7)` `authlib(8)` `courier(8)` `courierfax(8)` `courierfilter(8)` `courierldapaliasd(8)` `courierperlfilter(8)` `courierpop3d, courierpop3login(8)` `couriertcpd(8)` `courieruucp(8), makeuucpneighbors(8)` `dupfilter(8)` `esmtpd(8), esmtpd-msa(8)` | `imapd(8)` `mailq(8)` `makeacceptmailfor(8)` `makealiases(8)` `makehosteddomains(8)` `makepercentrelay(8)` `makesmtpaccess(8), makesmtpaccess-msa(8)` `makeuserdb(8), pw2userdb(8), vchkpw2userdb(8)` `mkesmtpdcert(8)` `mkimapdcert(8)` `mkpop3dcert(8)` `pop3d(8)` `submit(8)` `userdb(8)` `userdbpw(8)`

## Internal documentation (white papers)

The following stuff could be out of date, incomplete, or plainly wrong. An early version of these files were used for the initial design of the Courier mail server. As Courier was being developed, there were many slight changes from the original design. Hopefully, this documentation has been updated to reflect those changes... In some cases, stuff that's used to be here eventually migrated to the manual pages. This is a royal mess, you have been warned.

Directory Layout

Mail Queue

Transport Modules

Internal Structures

`courierd` Daemon Process

The `local` module

The `esmtp` module

The following documents describe Courier-specific ESMTP extensions.

The XEXDATA ESMTP extension is a useful extension to the format of the response to the DATA command, which allows for recipient-specified mail filters to be used.

The XVERP ESMTP extension allows for optimized distribution of mailing list messages with automatic bounce handling.

The XSECURITY ESMTP extension extends the existing SSL/TLS ESMTP extension to allow the implementation of a secure mail delivery infrastructure on top of an untrusted, public, network.