sudo apt-get install sendmail
sudo sendmailconfig

Apr 14 00:31:42 AY sendmail[32241]: NOQUEUE: SYSERR(www-data): can not chdir(/var/spool/mqueue-client/): Permission denied

sudo usermod -a -G smmsp www-data

groups www-data

www-data : www-data smmsp

smmsp:x:114:www-data

/var/spool]$ ls -la
total 28
drwxr-xr-x  7 root   root  4096 Apr  2 00:21 .
drwxr-xr-x 11 root   root  4096 Apr 14 03:30 ..
drwxr-xr-x  5 root   root  4096 Aug  6  2012 cron
lrwxrwxrwx  1 root   root     7 Aug  6  2012 mail -> ../mail
drwxr-s---  2 smmta  smmsp 4096 Apr 14 06:25 mqueue
drwxrws---  2 smmsp  smmsp 4096 Apr 14 06:25 mqueue-client
drwxr-xr-x  2 root   root  4096 Apr 13  2012 plymouth
drwxr-xr-x  2 syslog adm   4096 Mar 31  2012 rsyslog

/]$ ls -ld /var/spool/mqueue-client/ /usr/sbin/sendmail
lrwxrwxrwx 1 root  root    26 Apr  2 00:21 /usr/sbin/sendmail -> /etc/alternatives/sendmail
drwxrws--- 2 smmsp smmsp 4096 Apr 14 06:25 /var/spool/mqueue-client/

Apr 14 03:26:57 AY sendmail[6131]: NOQUEUE: SYSERR(www-data): can not write to queue directory /var/spool/mqueue-client/ (RunAsGid=33, required=114): Permission denied

www-data:x:33: