This is definitely a problem with the BT Infinity connection.
I have contacted hostgator who tell me they have run tests and cannot find any issues at their end.
This is supported by my own testing, the details of which follow. Hopefully this can be passed to someone technical at BT's end to investigate. If BT want to contact me I am perfectly willing to help in any way to get this resolved.
I created a new folder on my IMAP server, and stored some relatively large emails in there. These will be used to test the throughput.
I am using putty to manually connect to my IMAP email server:-
Connect to gator413.hostgator.com port 143 , standard IMAP.
Issue commands to login to the server and select folder Inbox.test
Issue command to fetch the body of message 1.
Use network monitor tool to view throughput of the IMAP connection.
Testing Results - Home Connection - BT Infinity
The data transfers from the Imap server in fits and starts, at some points I can see the data being displayed byte by byte. The network monitor tools shows speeds in the 2-10 k/s range, sometimes stopping altogether.
See image here:-
Testing Results - Office Connection - Demon Internet
The data transfers very quickly, almost too fast to get a screenshot of the network monitor tool. The network monitor shows speaks peaking at over 140k/s, at which point the body of the email has been transferred.
See image here:-
This seems fairly conclusive proof that something in the BT network is causing connections to this IMAP server to be very poor. Perhaps the IP range is caught up in some traffic management system? Maybe there is a very poor route in BT's network? I really don't know, and I do not know what other testing I can perform to highlight the issue. The above test is done at pure IMAP protocol level, removing any questions of a mis-configured or inefficient email client on my home PC.
Can this please be passed to someone technical at BT's fault team.