Hi,
Just some thoughts which might help.
* Disable all resident A/v scanning on the Wingate folder
* Unlikely, but is your link a PPP, have you tried lowering the MTU?
* No doubt you have tried different Auth' methods [if required] in the SMTP server
* Enable Wingate's firewall and disable / remove the other
* Definitely enable full debug logging in the SMTP server and post back how far it goes with the transaction to the remote gateway
Here is a sample log extract with debug enabled:
127.0.0.2 <system> 0000000413 Debug: ==== Attempting connection to mail.gateway.smtp.com[xx.xxx.x.xxx]
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 220 ESMTP Exim Sat, 17 Mar 2007 02:22:25 +0000
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: EHLO WINGATE
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250-mail.isp.co.uk Hello userhost.com
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250-SIZE 52428800
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250-PIPELINING
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250-AUTH PLAIN LOGIN CRAM-MD5
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250 HELP
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: AUTH PLAIN qw3r9pasucq9aufda9009hna9087poaoxvq90389q2
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 235 Authentication succeeded
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: MAIL FROM:<myemailaddress@mydomain.com.au> SIZE=857
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250 OK
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: RCPT TO:<customer@their.domain.com.au>
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250 Accepted
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: DATA
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 354 Enter message, ending with "." on a line by itself
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250 OK id=1HSOZ2-0004Rq-BS
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: RSET
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com <=S: 250 Reset OK
127.0.0.2 <system> 0000000413 Debug: mail.gateway.smtp.com C=>: QUIT
127.0.0.2 <system> 0000000413 Debug: ==== Server mail.gateway.smtp.com closed connection
127.0.0.2 <system> 0000000413 Traffic 1031 366 0 0 25s
127.0.0.2 <system> 0000000413 Terminated exit code 0
You can find the logs under C:\Program Files\WinGate\Logs\SMTP Server Server or thereabouts.