Jan 28 15:00:01 domain postfix/pickup[2452]: 2F81583C8B: uid=108 from=<smmsp>
Jan 28 15:00:01 domain postfix/cleanup[2765]: 2F81583C8B: message-id=<20140128150001.2F81583C8B@domain.co.uk>
Jan 28 15:00:01 domain postfix/qmgr[1881]: 2F81583C8B: from=<smmsp@domain.co.uk>, size=684, nrcpt=1 (queue active)
Jan 28 15:00:06 domain postfix/smtp[2767]: 2F81583C8B: to=<root@domain.co.uk>, orig_to=<root>, relay=mail.domain.co.uk[79.170.40.74]:25, delay=5.4, delays=0.01/0.01/5.3/0.05, dsn=5.0.0, status=bounced (host mail.domain.co.uk[79.170.4$
Jan 28 15:00:06 domain postfix/cleanup[2765]: 87F9F83C8C: message-id=<20140128150006.87F9F83C8C@domain.co.uk>
Jan 28 15:00:06 domain postfix/qmgr[1881]: 87F9F83C8C: from=<>, size=2663, nrcpt=1 (queue active)
Jan 28 15:00:06 domain postfix/bounce[2768]: 2F81583C8B: sender non-delivery notification: 87F9F83C8C
Jan 28 15:00:06 domain postfix/qmgr[1881]: 2F81583C8B: removed
Jan 28 15:00:06 domain postfix/smtp[2767]: 87F9F83C8C: to=<smmsp@domain.co.uk>, relay=mail.domain.co.uk[79.170.40.74]:25, delay=0.28, delays=0/0/0.24/0.03, dsn=5.0.0, status=bounced (host mail.domain.co.uk[79.170.40.74] said: 550 unk$
Jan 28 15:00:06 domain postfix/qmgr[1881]: 87F9F83C8C: removed

aptitude purge sendmail-bin sendmail-cf sendmail-doc