sieve sending vacation message from vmail@ns1.domain.tld

[Matthew Broadhead]

I have a server running centos-release-7-2.1511.el7.centos.2.10.x86_64 
with postfix version postfix-2.10.1-6.el7.x86_64 and dovecot version 
2.2.10.  I am also using roundcube for webmail.  when a vacation filter 
(reply with message) is created in roundcube it adds a rule to 
managesieve.sieve in the user's mailbox.  everything works fine except 
the reply comes from vm...@ns1.domain.tld instead of u...@domain.tld. 
ns1.domain.tld is the fully qualified name of the server.

it used to work fine on my old CentOS 6 server so I am not sure what has 
changed.  Can anyone point me in the direction of where I can configure 
this behaviour?

I read somewhere it might have something to do with a line in master.cf
dovecot   unix  -       n       n       -       -       pipe
flags=DRhu user=vmail:mail argv=/usr/libexec/dovecot/deliver -d ${recipient}

i changed it to
flags=DRhu user=vmail:mail argv=/usr/libexec/dovecot/dovecot-lda -f 
${sender} -d ${user}@${nexthop} -a ${original_recipient}

but it made no difference