Hi all, Solved my own problem shortly after posting earlier message.

Problem was my ISP decided to fire-fight spam and their IPs from blacklisting by blocking port 25. Duh!
http://www.jeffooi.com/2007/12/customers_cry_foul_over_tm_net.php

From what I see, they are not blocking all traffic but only from selected users.

Anyhow, used alternative port on Mercury. problem solved.

Hi, I am completely stump with this problem. Hope someone can give me a hand.

My setup is as follows :

1) Main office : Fixed IP address running Mercury Server - About 40 clients running thunderbird and outlook using IMAP/smtp.

2) Branch office : Dynamic IP - About 10 clients running thunderbird using IMAP/smtp connecting to Main office.

3) Homes : Dynamic IP - About 10 users connecting from home to Main office running IMAP/smtp.

Setup works fine for months. One fine day, branch office users is unable to send out mails. All users are able to connect to IMAP but unable to send.
- At that time, main office users and home users works fine.
- Thunderbird clients at branch office error message was unable to connect to smtp server.
- I used a notebook and tried sending from home - works. Used the same notebook plugged into the branch office network - failed.
- IP address issue maybe, reconnect the ADSL and got a new IP, still failed.
- Router problem maybe, connect the modem direct to notebook, bypass the router - still failed.
- Took back the notebook home - works. [:^)]

At the Mercury SMTP Server window and logs, I cannot see any messages for the failed connection from branch office.
At the meantime, I have changed the branch office clients to use the ISP smtp server.

Any help is appreciated.