OK, I found out what the problem was - stunnel was not running! There was nothing in the log to indicate that it was shutting down. Started it up again and everything started to work as before. One thing I have noticed is that in Mail.app I have to turn on ‘Allow insecure authentication’ as otherwise it will give up after ages, saying that the certificate is invalid. 2015.03.31 11:06:17 LOG7[main]: Service [ssmtp] accepted (FD=3) from 192.168.1.10:56364 2015.03.31 11:06:17 LOG7[26]: Service [ssmtp] started 2015.03.31 11:06:17 LOG5[26]: Service [ssmtp] accepted connection from 192.168.1.10:56364 2015.03.31 11:06:17 LOG7[26]: SSL state (accept): before/accept initialization 2015.03.31 11:11:17 LOG6[26]: ssl_start: s_poll_wait: TIMEOUTbusy exceeded: sending reset 2015.03.31 11:11:17 LOG5[26]: Connection reset: 0 byte(s) sent to SSL, 0 byte(s) sent to socket 2015.03.31 11:11:17 LOG7[26]: Local socket (FD=3) closed 2015.03.31 11:11:17 LOG7[26]: Service [ssmtp] finished (0 left) Mail.app simply logs this: 31/3/2015 11:06:17.520 am Mail[3172]: CFNetwork SSLHandshake failed (-9807) The client is running Yosemite 10.10.3 latest beta. Any ideas why it would think it is invalid? Any way to find out? Thanks, James.