If you are just sending outbound emails this way, use ssmtp rather than sendmail.
It's *roughly* as follows
yum install ssmtp
alternatives --config mta # select the number for /usr/sbin/sendmail.ssmtp
>> #add a line to the file like ...
>> # you need to add gmail authentication info
>> # see example here http://wiki.debian.org/sSMTP
The outbound mail is only sent when activated by a use of sendmail (from 'mail' or 'mailx' for example. There is no constantly running service.
---------- Post added at 09:33 AM ---------- Previous post was at 09:29 AM ----------
I think you need this for gmail setup of ssmtp
But if you are using google+ you *may* need to generate one of those app specific passwords. Not sure.
Sendmail is way overkill.