конфиг:

UseIPv6                         off
AllowOverwrite on
AuthAliasOnly on
UserAlias user mama

ServerName          "11"
ServerType          standalone
DeferWelcome            on

MultilineRFC2228 on
DefaultServer           on
ShowSymlinks            off

TimeoutNoTransfer 600
TimeoutStalled 100
TimeoutIdle 2200

DisplayFirstChdir               .message
ListOptions                 "-l"

RequireValidShell       off

TimeoutLogin 20

RootLogin           off
ExtendedLog             /var/log/ftp.log
TransferLog             /var/log/xferlog
SystemLog           /var/log/syslog.log

UseFtpUsers off

AllowStoreRestart       on

Port                21

MaxInstances 8

User                  nobody
Group                 nogroup

Umask               022 022

PersistentPasswd        off
MaxClients 8
MaxClientsPerHost 8
MaxClientsPerUser 8
MaxHostsPerUser 8

DefaultRoot ~

MaxLoginAttempts    5

<Limit LOGIN>
AllowUser mama
DenyALL
</Limit>

<Directory /home/mama>
Umask 022 022
AllowOverwrite off
<Limit MKD STOR DELE XMKD RNRF RNTO RMD XRMD>
DenyAll
</Limit>
</Directory>

<Directory /home/mama/public>
Umask 022 022
AllowOverwrite off
<Limit MKD STOR DELE XMKD RNEF RNTO RMD XRMD>
DenyAll
</Limit>
</Directory>

проверяемс:
root@jaybee:~# ftp
ftp> o localhost
Connected to localhost.
220 ProFTPD 1.3.1 Server ready.
Name (localhost:root): user
331 Password required for user
Password:
230 User user logged in
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
200 PORT command successful
150 Opening ASCII mode data connection for file list
226 Transfer complete
ftp> bye
221 Goodbye.

root@jaybee:~# ftp
ftp> o localhost
Connected to localhost.
220 ProFTPD 1.3.1 Server ready.
Name (localhost:root): mama
331 Password required for mama
Password:
530 Login incorrect.
Login failed.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> ls
530 Please login with USER and PASS
ftp: bind: Address already in use
ftp>

какбэ то, чего хотели

логи:
localhost 0 nobody [20/Mar/2009:17:31:27 +0200] "USER user" 331 -
localhost 0 mama [20/Mar/2009:17:31:28 +0200] "PASS (hidden)" 230 -
localhost 0 mama [20/Mar/2009:17:31:28 +0200] "SYST" 215 -
localhost 0 mama [20/Mar/2009:17:31:29 +0200] "PORT 127,0,0,1,139,173" 200 -
localhost 0 mama [20/Mar/2009:17:31:29 +0200] "LIST" 226 0
localhost 0 mama [20/Mar/2009:17:31:46 +0200] "QUIT" 221 -
localhost 0 nobody [20/Mar/2009:17:31:52 +0200] "USER mama" 331 -
localhost 0 nobody [20/Mar/2009:17:31:53 +0200] "PASS (hidden)" 530 -
localhost 0 nobody [20/Mar/2009:17:31:53 +0200] "SYST" 215 -
localhost 0 nobody [20/Mar/2009:17:31:54 +0200] "PORT 127,0,0,1,209,80" - -

выше я привел манипуляции с вашим конфигом

>
>cat proftpd.conf | grep UserAlias
>UserAlias donet user
>
>UserAlias [алиас(donet) реаднейм(user)]
>
>Шеф, может не в ту область ушли?

читая ваш конфиг я понимаю обратное
юсер - алиас
донет - реалюзик

доказательства
а)
UNKNOWN nobody [20/Mar/2009:17:40:48 +0500] "USER user" 331 -
UNKNOWN nobody [20/Mar/2009:17:40:48 +0500] "PASS (hidden)" 530 -
UNKNOWN nobody [20/Mar/2009:17:40:48 +0500] "QUIT" 221 -
б)
AuthAliasOnly on