email - Linux Send Mail - Command Line

I have a little script on Centos 6.5 64 bit which sends
email content of a text file (as inline and NOT as attachment) to a
user:

mail -s "Zabbix Alerts" -r
            sender@mydomain.com receiver@mydomain.com <
            /filename

It
used to work great for a long time. Today we have got a new server Centos 6.7 64bit and
the same scripts sends what is expected but not as inline but as
attachment.

We need the content of the text file
as inline text (not attachment).

I have already
spent a few hours find the cause but no luck.

I
will be really thankful if someone can help me.