Hi Bruce

 

Thanks for your input.

 

Have checked that setting and it has a correct IP address assigned - doesn't seem to have a bearing, issue persists

 

if webmail login works, than outlook must be the culprit?

Could also be that port 25 is blocked for SMTP clients, by the user's ISP -- not at all uncommon these days

Make certain you have port 587 mapped and avaliable,  and have them try their SMTP connection for the client on port 587.
See:

https://portal.chicagonettech.com/kb/a104/blocking-of-alternate-smtp-port-587-by-isps-now-prohibited.aspx

for more information.

Hi All

 

Thanks for the ideas - SM is on our own dedicated Server.

 

We have tested this issue in Outlook from a number of different PCs/locations with the same result

 

Seems this specific domain is being routed via a 3rd party dynamic DNS.  Aparently their Server was updated recently and we suspect this is causing the issue

 

We are waiting to hear from their support people but i'm "quietly confident" this is the problem

 

Thanks again

 

From what Graham said, it seems as if the server does have a static IP, but the DNS routing is some form of dynamic arrangement. 

 

I have this (successful) situation with Symantec Email Security.cloud filtering. They process incoming and outgoing emails and relay them to/from Smartermail and other email servers that I maintain.  "cluster5.us.messagelabs.com", for example, is in the MX record. They give this, or variations on this, to different accounts. The secondary MX entry would be, for example, "cluster5a.us.messagelabs.com".

 

Outgoing emails are sent from this cloud service using one of many outbound IP addresses - yes they do change all the time - and this routing works just fine.

 

I've been using this service for several years (back then it was called Messagelabs). Interested to know the final resolution of Graham's issue.

 

 

 

Thanks for all the input and comments

 

Our server does have a fixed IP.  The present DNS routing via a 3rd party is purely for flexibilty reasons, no mail security reasons or such like.

 

We are in the process of changing the domain settings to bypass the present DNS routing and route directly to our name servers/server

 

We are confident this will resolve the issue