Sending email to all over the world, especially to China, is a big challenge. How to deliver email safely and lower the bandwidth consumption?
Here is my recipes.
Standard SMTP need a lot of conversations, to finish ONE email message. So, for long distance transaction, I’ll make use of QMQP (Quick Mail Queueing Protocol) which is a lot faster than standard one.
To identify country, I’ll use GeoIP from MaxMind. You can subscribe the paid service to keep your database up-to-date, or I will simply use GeoLite (Country) which is less accurate (96%?) , but good enough for us.
Postfix is highly configurable MTA, I use it because it support QMQP (only for receiving email…)
Qmail (mini version):
Yes, I use two MTA, because Postfix doesn’t implement QMQP client.
Although QMQP use tcp port 628, I may use OpenVPN to secure the traffic.
Scripting is needed