If you get the problem below, trimmed and highlighted in bold:
SASL authentication failure: cannot connect to saslauthd server
At least run the command below to see if the service is started:
service saslauthd status
Full log example:
Dec 7 10:30:49 eyou postfix/smtpd[3843462]: connect from unknown[a.b.c.d] Dec 7 10:30:49 eyou postfix/smtpd[3843462]: warning: SASL authentication failure: cannot connect to saslauthd server: No such file or directory Dec 7 10:30:49 eyou postfix/smtpd[3843462]: warning: unknown[a.b.c.d]: SASL LOGIN authentication failed: generic failure Dec 7 10:30:49 eyou postfix/smtpd[3843462]: lost connection after AUTH from unknown[a.b.c.d] Dec 7 10:30:49 eyou postfix/smtpd[3843462]: disconnect from unknown[a.b.c.d] ehlo=1 auth=0/1 commands=1/2
Note also generic failure