Ok so is no confusion the issue isnt a slow connection to the mail server or slow to submit email it is a low throughput. Since normal emails are tiny they go fast but if I eg. send a 1meg file over smtp email it is slower than eg. ftp.
My connection is 20mbit upload so approx 2.4mbytes upload so no confusion.
So my web server which I manage is my primary email server, it also has ftp as a transfer protocol. As well as a webmail interface.
If I upload the file to the ftp it uses all my upstream bandwidth.
If I send an email with the file as an attachment using webmail it uploads and is sent in under a second.
If I send the email via smtp using outlook it sends at around 200kB/sec.
The following all have no affect on the speed other than stated.
Changing the smtp port.
Enabling ctcp increases the speed to 250kB/sec, which is still hideous barely over 10% of my possible speed.
I havent tried another email client such as outlook express or thunderbird, or outlook 2010.
I suspect the issue is that outlook is hardcoded to a small tcp send buffer as a typical end user doesnt have a fast upload connection when outlook 2007 was developed. If so is there a way to tune it higher (or is it really hardcoded non tunable) or is there other ideas to speed it up.