RFC 2822 describes how long header lines in email should be "folded". The
short of it is that a newline should be inserted just before a space in the
subject. This results in something like

|Subject: blah blah
| blah blah blah

which is recognized as a folded header because the second line of the
header starts with linear whitespace. The RFC also discusses how to
"unfold" such a header: just remove the newline on the initial line of the
header. This means that the above is effectlely the same as

|Subect: blah blah blah blah blah

However, GW does more than insert a newline, it also indents the folded
material with a tab character:

|Subject: blah blah
|<tab> blah blah blah

RFC-compliant clients see such a header and think that the subject is

|Subject: blah blah<tab> blah blah blah

This is a standards-compliance failure and a bug in GW.

It isn't clear to me whether it's on the server end or the client end, or
both. I just know that when I see email threads at work between GW and
non-GW users, the tab insertions get quite out of hand as they get inserted
by GW users and treated as litterals by non-GW users, and then the GW users
include both the litteral tabs and insert some more gratuitous tabs as they
wrap the subject line in a new place.

The patch to correct this should be small.

See section 2.2.3 of RFC 2882