Email "Unpacking" Problem ?

[canarytops]

Hello, for about 6 months whenever a colleague replies (with history) to one of my emails all I receive is the text of my original email shown as having been sent by my colleague. It is as if his reply has been ignored. I have seen such an email as copied to a third party and he is definately replying (!).
Are there any particular control strings/syntax rules that the Virgin webmail servers employ that could cause this "header" deletion ?
This has just started to happen to another colleague's emails so I thought I'd raise in the hope someone might know what's going on.
If either send me an email I receive them OK.
Bother work for (different) large corporates who employ Notes Exchange servers. I can communicate whith other people from both sites without any problems !