Our Exchange 2003 server isn't recieving emails from a certain domain.

richiewilmot
richiewilmot used Ask the Experts™
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Our Exchange 2003 server doesn't recieve emails from the domain ufi.com especially when those emails have attachments of any size. I have checked and attachments are allowed. Incoming emails from my google and hotmail account work fine as do outgoing emails to hotmail and google. Outgoing emails from our domain also appear to work fine.

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Just some common things to check on this:

1.) I assume you have a proper revers on your domain?

2.) Verify that your domain is not on a black list.

3.) I noticed that ufi.com is pushing there mail through message labs, it is possible that message labs is blocking them from sending to you.
SurajSenior System Engineer

Commented:
especially ? is it mails with attachment from those domains or all ?
please be clear coz it makes a big difference in troubleshooting...
do you get any NDR on domain ufi.com  domain when a use sends from there?
It doesn't matter if you domain is blacklisted, they will still be able to send to you, you just may not be able to send to them.  Same for reverse PTR records for your domain.  This all has to do with sending, which you are not having problems with.  Also, just becuase ufi.com's MX record point to message-labs, doesn't assume that ufi.com's mail server relays their outbound mail through them as a smarthost or bridgehead server.  The only way to determine that is by looking in the message header for an email that originated from UFI to some outside email address.

Do MX records for your domain point to you or some cloud SPAM filtering service?  This will help us help you get to the bottom of this issue you are having.

Have someone from UFI.com try to telnet to your mail server on port 25 - telnet xxx.xxx.xxx.xxx 25 (do they get a banner or are they denied access, could be IPS/firewall related).

If MX points directly to your mail server, try looking in the firewall logs when they send you an email.  Make sure you know what IP they will be coming from and filter on TCP 25.

Please report back all information you have gathered and we should be able to point you in the right direction.

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Author

Commented:
Thanks ever so much for the information guys, most of it I understood but some of it I didn't as I am fairly new to all this. I think the MX records are correct and our domain is not on a blacklist (111 known lists checked).

Also, we appear to be receiving emails that either no attachments or very small attachments. My boss has said that it appears to be only mails with large attachments (5-10MB).

Thanks for the help so far guys, you've been great. Please accept my apologies for the lack of experience/knowledge!
SurajSenior System Engineer

Commented:
whts the message size set on the server?
you need to check that on store, smtp virtual server and also on the user...

Author

Commented:
There currently isn't a limit on message size in the store, smtp virtual server or on the user.
SurajSenior System Engineer

Commented:
well... to be honest.. this is a bad practice.. i mean very bad... the reason being...
what if any user sends a 1-2 Gb of attachment mail?
your server will crash.. so put some limit. on it... this is nothng to do with your issue now but just an advice...
do you have a firewall? whats the MTU value set on it? or a router ?
how is your inbound mail flow configured???

Author

Commented:
Yes I agree with it being bad. My boss has recently purchased this new centre in Cambridge and there was someone else looking after the server, but they called him in once in a while and he did everything else remotely. I will put a limit on it.

Yes we have a firewall, Cisco Pix 501 I believe. And I think the MTU value is set to 1500.

Please clarify "how is your inbound mail flow configured???".
SurajSenior System Engineer

Commented:
i mean... is it somethng like..

Internet --> spam filter--> firewall --> exchange srver ??

do you have any 3rd party app on the srver for spam filtering or an AV?
disable them or remove them and check if that works out

Author

Commented:
I would say thats about right.

We have a hosting package with bignames.co.uk that includes email and so I would assume that it goes through them first, then to our firewall, to the server (which has Sophos AV) then to the exchange mailboxes.

Something to consider? Our AV has expired and we are in the process of replacing it, would the expired AV cause this?

Does that help and Thanks for your patience.
Well, if you are using another service to intercept the mail first, then re-route the mail to your mail server, then they more-than-likely have some type of size limitation on the message size.  Since you do utilize a third party service, contact them to see if they see these emails coming through.  See if they are dropping the connection or just deleting based off content of reliability of sender.  

Consider this as well.  If you use a third pary mail filter, then you should have inbound source rules on your firewall to only allow their IP addresses/ranges to connect to your mail server on TCP 25.  Make sure this list is currect while you have them on the phone.  This can help be proactive for future issues.
SurajSenior System Engineer

Commented:
just uninstall your AV

Author

Commented:
I have contacted the hosting people and am now awaiting their response with regards to this issue. It really has been the biggest pain in the ass.. I have increased the points again too, I really badly want this sorted!

Thanks for your help guys.

Author

Commented:
Sorry for keeping this open guys, having lots problems with various other things and will get back on this very soon.

Author

Commented:
Hosting people have no restrictions on mail size. I reconfigured a few things in exchange and it now seems to be ok.

Thanks to everyone for their help and patience with this, really appreciate it.

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