fixing / changing HELO of mail server

Bounce processing was not proceeding. It complained that php imap module was not installed. Did

apt-get install php5-imap

and service restart apache2

Then error was, cannot open /var/mail/apachemails

Checked
http://hnsws.blogspot.in/2011/04/bounce-processing-cleanup.html

had to do chmod 660 for /var/mail/apachemails

Some mails are being bounced, like rediffmail,
Jan 10 02:19:32 krishna postfix/smtp[28562]: 112D02A0C11: to=, relay=mx.rediffmail.rediff.akadns.net[119.252.147.10]:25, delay=0.27, delays=0.1/0/0.1/0.07, dsn=5.0.0, status=bounced (host mx.rediffmail.rediff.akadns.net[119.252.147.10] said: 553 sorry, invalid HELO hostname (#5.7.1) (in reply to RCPT TO command))

Checking the sai inspires email, looks like the HELO is being sent as krishna instead of FQDN, gmail show original shows

Received: from krishna.radiosai.org (krishna.radiosai.org. [111.93.16.162])
        by mx.google.com

for older mails, while for newer mails it says

Received: from krishna (krishna.radiosai.org. [111.93.16.162])
        by mx.google.com

Fixed by changing in /etc/postfix/main.cf
 myhostname=krishna   to
 myhostname=krishna.radiosai.org
using
https://major.io/2006/12/26/fixing-invalid-helos/