How to get ssmtp to map local user to email address for the To: field

I have struggled a bit with ssmtp too. The first thing I learned is that the aliases mechanism does not work with the plain mail program; I have to use mailx from the package bsd-mailx — never knew why. So before starting to change configurations around check with it.

Anyway, as a reference, I have a working ssmtp setup like the following:

1. file /etc/ssmtp/ssmtp.conf:

   #
   # Config file for sSMTP sendmail
   #
   # The person who gets all mail for userids < 1000
   # Make this empty to disable rewriting.
   [email protected]
   
   # The place where the mail goes. The actual machine name is required no 
   # MX records are consulted. Commonly mailhosts are named mail.domain.com
   mailhub=mymailserver.mymail.domain.com:25
   
   # Where will the mail seem to come from?
   rewriteDomain=mymail.domain.com
   
   # The full hostname
   hostname=myhostname.mymail.domain.com
   # Use SSL/TLS before starting negotiation 
   UseTLS=No
   #UseSTARTTLS=Yes
   #
   # Are users allowed to set their own From: address?
   # YES - Allow the user to specify their own From: address
   # NO - Use the system generated From: address
   FromLineOverride=NO
   

2. file /etc/ssmtp/revaliases/

   # sSMTP aliases
   # 
   # Format:   local_account:outgoing_address:mailhub
   #
   # Example: root:[email protected]:mailhub.your.domain[:port]
   # where [:port] is an optional port number that defaults to 25.
   #
   root:[email protected]
   romano:[email protected]
   postmaster:[email protected]
   

and now it works:

[romano:~] % mailx -v root
Subject: test
test
.
Cc: 
[<-] 220 mymailserver.mymail.domain.com ESMTP my mail server
[->] HELO myhostname.mymail.domain.com
[<-] 250 mymailserver.mymail.domain.com
[->] MAIL FROM:<[email protected]>
[<-] 250 2.1.0 Ok
[->] RCPT TO:<[email protected]>
[<-] 250 2.1.5 Ok
[->] DATA
[<-] 354 End data with <CR><LF>.<CR><LF>
[->] Received: by myhostname.mymail.domain.com (sSMTP sendmail emulation); Fri, 03 Jul 2015 13:25:52 +0200
[->] From: "Romano Giannetti" <[email protected]>
[->] Date: Fri, 03 Jul 2015 13:25:52 +0200
[->] To: root
[->] Subject: test
[->] 
[->] test
[->] .
[<-] 250 2.0.0 Ok: queued as BF1CB3BC050
[->] QUIT
[<-] 221 2.0.0 Bye

Notice that domains, hostnames etc. are scrambled for privacy here (so there can be typoes).