IIS SMTP Queue Stuck

1. Review SMTP logs in C:\Windows\System32\LogFiles\SMTPSVC1,

2. Find 421 Error

2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 109 SMTP----
2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 109 SMTP----
2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 109 SMTP----
2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 94 SMTP----
2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 94 SMTP----
2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 94 SMTP----
2014-12-08 02:02:40 212.118.102.234 outboundconnectionresponse SMTPSVC1 smtp1-25--421+service+not+available,+ Closing+transmission+channel 0 0 0 94 SMTP----

3. Check this IP

Nslookup 212.118.102.234
Server:server1
address:192.130.74.51

Name:mail.zahid.com
address:212.118.102.234

4. Telnet port for the server on SMTP, return 421 error

421 Service not available, closing transmission channel

Connection to host lost.

5. Telnet port for the server on the other server, return connection, established.

xshell:\> Telnet 212.118.102.234 25

Connecting to 212.118.102.234:25 ...
Connection established.
To escape to local shell, press ' ctrl+alt+] '.
220 *************************************************

6. So 212.118.102.234 block our SMTP external IP address, and many emails is in the queue to the ready to delivery again ....

refer:http://simplydotnet.wordpress.com/2010/08/11/outgoing-email-stuck-in-queue-folder-iis-smtp-server/

IIS SMTP Queue Stuck