Some but not all incoming emails are being bounced

do a spam check on your public ip, if it is blocked. www.dnsstuff.com

see if this tool shows valid rdns record for ur domain
http://www.postmaster.aol.com/tools/rdns.html

checked the blaclists using MXTOOLBOX.com & all ok
Have run the RDNS test & the response was:
DNS Server Response:
mailgate.philippank.com

Success! It appears you have Reverse DNS.

Does this happen to a particular internal email id? or all internal email id?
Did anyone configured exchange recently?
Do you have any email security, did you check on it if things are ok?

Its happening from approximatle 10 outside customer domains, to numerous internal email addresses. We can send emails to them but when they try to reply they get the helo/ehlo message
Our exchange server has not been touched in any way.
We run GFI mail security & mail essentials, both of which have been running for the last 3+ years with no problems

Can you verify setting with solution mentioned in this link
https://www.experts-exchange.com/questions/23037415/HELO-EHLO-domain-invalid-error-on-Exchange-2003-server.html

Also read this
http://www.irbs.net/internet/postfix/0502/1574.html and verify

The settings are exactly as https://www.experts-exchange.com/questions/23037415/HELO-EHLO-domain-invalid-error-on-Exchange-2003-server.html 
Our firewall has anti spam on it & the black list is empty & again has been in place for ages.

Did you try to restart exchange services? If that doesnt help, you would like to wait till others suggest something.

I have restarted the server numerous times & just the services but it still happens.
could it be that their server names do not match their DNS/MX records & thas why I reject them?

mailgate.philippank.com is this ur domain name actual one?
can i know which domains gets bounced back? give atleast couple of them.

mailgate.phiolippank.com is the FQDM

domains that are getting emails bounced back are:
onehousinggroup.co.uk
gleeds.co.uk
hanover.org.uk

All these were ok up to sunday last weekend.
Again I reiterate that no software changes have been made on our filrewall or our server.....

getting urgent....pionts increased !!

Is this your mail server public ip?
62.244.172.90

I ran almost 5 to 6 different test on your domain and ip, and all came successful.
Lastly i would like to know if you can paste the exact error whenthe mail is bounced.
Yes, you will have to ask to the person whose email got bounced sending to your domain. get atleast 2 for a quick solution. Call them and ask them to forward that bounce back error to your some other domain account (for, eg hotmail.com).

The error should hav some kind of code with the error message.

The message that all the 10 or so are getting back when they try & send an email is:
host mailgate.PhilipPank.com[52.244.172. 90)
said: 5545.7.1 This message has been blocked because the HELOjEHLO domain
is invalid (in reply to RCPT TO command)
62.244.172.90 is our mail server public ip
mailgate.philippank.com is our FQDN on the email server

Who's ip is this 52.244.172. 90?
Seems like people who's emails are bouncing has your servers wrong ip in their dns cache as 52.244.172. 90 rather then 62.244.172.90.

That ip belongs to a server in the USA...
OrgName:    E.I. du Pont de Nemours and Co., Inc.
OrgID:      EDPDNC
Address:    E.I. du Pont de Nemours and Co., Inc.
Address:     1007 market Street
City:       Wilmington
StateProv:  DE
PostalCode: 19893
Country:    US
NetRange:   52.0.0.0 - 52.255.255.255
Why do you think their DNS is incorrect? how did you test it?
I have asked that they clear their cache...but the only way seems to work is to get them to change their FQDN to match their MX record & some are quite reticent to do so as it worked ok before....
What I don't understand is what caused my server to start bouncing stuff? As nothing had changed on my side at all.

>>>Why do you think their DNS is incorrect? how did you test it?
Because if you see this message "mailgate.PhilipPank.com[52.244.172. 90)", i assume your mail server ip is wrong on their end.

They dont have to do except clearing their cache. If email sent to you from hotmail or gmail, does it works fine?

I think that is a red herring user typo maybe.
I have attached a copy of message from a fax I have recieved
latest-error.pdf

ESM, Servers, , Protocols, SMTP. Right click on the default SMTP VS and choose Properties. Click on the tab Delivery and then Advanced.
what is the value over there?

Max hop count = 30
Masquerade domain is blank
Fully qualified domain name is mailgate.philippank.com
smart host is blank
Perform remote dns lookup on incoming messages is blank (it was ticked but have unticked it to see if it made a difference)

Points value has increased

I think you need to wait till someone further helps ahead.
One last try, do one thing.
In your email security whitelist the domain name which is having problem and see what happens.

I'd already added the domains that have the issue to the whitelist & that had no effect.

Maximum points now

If you click test mail server here
http://mxtoolbox.com/diagnostic.aspx?HOST=mailgate.philippank.com

Everything looks good.

ESM, Servers, , Protocols, SMTP. Right click on the default SMTP VS and choose Properties. Click on the tab Delivery and then Advanced.

There is a button to click which says check dns. if clicked what does it say?

The domain nmame is valid is the response
I have run the same test  on those domains that are failing & all are ok as well...

Did you check your firewall configuration for smtp rule? i hope it is not modifying any default incoming packets.

Firewall rules have not been changed for over 3 months.
Its not happening with all inbound emails, a lot get through with no problem, but the majoirity that are being bounced are from other exchange servers. So I have been asking thatthey check that their FQDM on their exchange server matches their mx record.

Can you goto your esm, default smtp connector, properties, advanced tab, there is a chekbox which says 'send helo instead of ehlo..." is that check box selected?

Yes it is
We're bouncing the messages back beacause the senders domain is invalid not ours I've added them to our AV whitelists etc but has made no difference at all.

uncheck the box, it should not be selected
Once done see if the problem still remains.

alternatively you can also try to disable your email security software for a while and see if the problem is still there.

the box is unchecked & it is still happening

ok

hahaha Great  it got resolved finally.