I am using Microsoft's IIS SMTP service to relay email from within my network. Essentially, emails of between 100K and 10MB are sent to one of two Server 2008 machines on the local subnet, and then forwarded to one of several email servers outside our subnet. The emails originate from internal devices such as scanners. All emails are sent with TLS enabled, and a check of the header shows that the emails are secured and there appear to be no unexpected intervening stops.
The problem is that sending the emails is extremely slow. The SMTP service sends only one email at a time, and it is send very slowly. This results in potentially long delays. I can see no settings that will speed up the SMTP service.
It is possible that the email receiver is causing the delays. I would like to:
1. Have the SMTP service send multiple emailssimultaneously, or
2. If someone could suggest an easy-to-maintain, low overhead SMTP server to install. I have tried a few, but configuration can be quite complex as the SMTP servers I ahve looked at are designed to receive emails, something I don't need to do.