Notes/Domino 6 and 7 Forum : Garbled Incoming Email

We're getting garbled email coming in from a certain (important) client.

What should I look for in troubleshooting this issue?

Below is an excerpt from one such garbled email from that person (excerpt
meaning that where I go {<snip!> etc.... ] I left out about 50 lines of the
FkYQ0K crap.)

I note that this one email seemed to have two parts to it, text/plain; and
text/html; but not sure if that's got anything to do with the price of tea in
China.

_________________

Content-Type: multipart/alternative;

boundary="_000_71D1BD33B57D864FB7CC652F3303900B16929437A0BMFGEXCMB03ad_"
Content-Language: en-US

--_000_71D1BD33B57D864FB7CC652F3303900B16929437A0BMFGEXCMB03ad_
Content-Transfer-Encoding: base64
Content-Type: text/plain; charset="utf-8"

2VlIHlvdSB0aGVyZSENCg0KTmFkYQ0KDQpfX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f
Xw0KRnJvbTogbW1hcnJAYWN0b3JvbnRvLm9yZyA8bW1hcnJAYWN0b3JvbnRvLm9yZz4NClRvOiBS
aXN0aWNoLCBOYWRhDQpTZW50OiBUdWUgSmFuIDEyIDE5OjM4OjUyIDIwMTANClN1YmplY3Q6IEx1
bmNoIHdpdGggTWljaGFlbCAmIE1lcmVkaXRoIHRvbW9ycm93DQoNCkhpIE5hZGE6DQoNCldlJ3Jl
{<snip!> etc.... ]

--_000_71D1BD33B57D864FB7CC652F3303900B16929437A0BMFGEXCMB03ad_
Content-Transfer-Encoding: base64
Content-Type: text/html; charset="utf-8"

PGRpdj48Zm9udCBzaXplPTIgY29sb3I9bmF2eSBmYWNlPUFyaWFsPg0KU2VlIHlvdSB0aGVyZSE8
YnI+PGJyPk5hZGE8L2ZvbnQ+PC9kaXY+DQo8YnI+PGRpdj48aHIgc2l6ZT0yIHdpZHRoPSIxMDAl
IiBhbGlnbj1jZW50ZXIgdGFiaW5kZXg9LTE+DQo8Zm9udCBmYWNlPVRhaG9tYSBzaXplPTI+DQo8
{<snip!> etc.... ]