some of our members here have problems sending to addresses at BTinternet.com

they get an I/O error message

our message has encountered delivery problems
to the following recipient(s):

[email protected]
Delivery failed


Failed to deliver to domain btinternet.com after 1152 tries. Last
error was: I/O error encountered

or just delivery failure
and then all emails arrive several days later and at the same time.

there are at least 6 addresses that i know personally that are effected and others here report it too.

I have verified all the addrresses i know of problems with on the www.network-tools.com email validation program, and users of other ISPs (and ive verified thsi too) CAN send to the BTinternet.com adrresses with no problems.
our sysadmin team doesnt reply to my emails about it (im only first line, what do i know?) and im getting some very angry customers calling me and i cant give them answers.

HELP!