Using talktalk web mail, when I send a message to a large group of contacts from my address book, I get some recipients' servers complaining something like the following:
BAD HEADER SECTION, Improper folded header field made up entirely of whitespace
This is followed by some detail: the 'To:' header appears to get some tab and newline characters inserted between addresses in the list like
<person1@site2.com>,\n \t \n\t<person2@site2.com>
As far as I can tell, at the point of composing the message does not have these extra characters in it and the contact's address (person2 in this example) does not have these characters.
This looks like a bug in the web mail handling of groups?