Invalid Email Addresses cause 4.0.8 to stall

Hello,

Just a heads up that I have now received two pieces of spam which appear to have invalid From: addresses in the header which 
cause Mulberry to hang.

The initial part of the inbound Russian message From: field is :

Исаков <=?koi8-r?B?IOHMxcvTxcXXIDw9P2tvaTgtcj9CPzVzWEUwU0RoenNuVHljM1AxeQ==?= 
=?koi8-r?B?QThQVDlyYjJrNExYSS9RajlKVUV4YWQzTklUSG81WTJkUVJBPT0/PQ==?= 
=?koi8-r?B?CT0/a29pOC1yP0I/TUM5aE1qbHdUME14ZVZBd1NTOU9SMDQyVW01cg==?= 
=?koi8-r?B?TlZWRldqVmhWVkoxVFVoT2RWTklielZVUVE9PT89CT0/a29pOC1yPw==?= 
=?koi8-r?B?Qj9QVDAvUFFrOVAydHZhVGd0Y2o5Q1AxZFlhR3RaTW1SUlVrUkJkbA==?= 
=?koi8-r?B?bFVTVFZqUlRsRVRWaHNVUT09Pz0JPT9rb2k4LXI/Qj9UVVZyZGxRdw==?= 
=?koi8-r?B?VlhoVFZtUkpZVWR3YTAxdFRYZFpNMk01VUZRNE9VTlJQVDAvUFFrOQ==?= 
=?koi8-r?B?UDJ0dmFRPT0/PQk9P2tvaTgtcj9CP09DMXlQMEkvVUZRNWNtSXlheg==?= =?koi8-r?B?

and it carries on for another 200 lines.

My only option was to delete it from a webmail client (actually I have put it somewhere safe in case anyone wants to spend more 
time looking at the cause).

Raza