Question : Mails sent from outlook not being received by recepients in one domain only

Our mail hosting is done by a particular service provider.  Ever since we had them hosting our emails we find our mails not being received by our vendor.  This is erratic.  somedays it will work just fine and somedays the mails will just not go.  No "undeliverable message"is also received by us.  We have tried the following steps but to no avail:
- changed the ISP whose broadband connection we were using - no change
- changed the mail hosting provider of one or our domains - no change
-escalated this to the IT department of our vendor, who claims to have no blocking mechanism for our domain dotcad.in or dotcad.co.in.

we are at our wits end on what do do now.  URGENTLY need help on understanding what can be done.

Answer : Mails sent from outlook not being received by recepients in one domain only

*** Mmmmm, their IT department might ignore they have one. Example if it's a small company with hosted e-mails service. They will tell you they don't block anything, but their provider / hosted-service provider (call them what you want) will for them.

You appear in a few blacklists, check here: http://www.dnsbl.info/dnsbl-database-check.php
I used your 2 IPs:
dotcad.in               A       202.137.237.27
dotcad.in               A       202.137.236.10

This one was ok:
dotcad.co.in            A       74.53.251.150

If their provider uses this lists, you might be blocked.

Where are you e-mail sent from? from one of those 3 IPs ? or from your something else ? your MX for dotcad.in is some third-party company I guess (mail.rediffmailpro.com) and for dotcad.co.in, it seems to be a fourth IP/host (74.55.15.98)
Some e-mails servers don't like mails sent from @one.domain relayed from an host whose FQDN is not "one.domain"

*** Ask your vendor to check their logs and look for incoming connections from the IP you are sending your e-mails from, I'm sure they'll see your connection attempts and their log might explain why it's being silently rejected. Or it's a connection problem, but they would have this problem with some other company they communicate with, I guess.



I hope these are some ideas that will help

Regards