[Dovecot] SSL warning messages

Hi,

I've had the following appear in my logfile, and am just wondering what the warning means?

dovecot: managesieve-login: Warning: SSL alert: where=0x4008, ret=256: warning close notify [a.b.c.d] dovecot: imap-login: Warning: SSL alert: where=0x4004, ret=256: warning close notify [w.x.y.z]

Should I be worrying about these kinds of messages?

Dovecot 2.2.4 on Ubuntu 12.04 LTS if it is important.

Thanks, Anand