We have been converted without choice to a Microsoft Exchange proprietary email server, although IMAP service has been retained. I have 64 bit X86-64 Thunderbird on my office machine, and 32 bit IA-32 Thunderbird on my laptop, both under SL6x (64 bit office, 32 bit laptop). The office machine is 4 core, my laptop is 2 core. On my office machine, when using the MS IMAP server, Thunderbird runs very, very slowly, with a single core reported load over 100 percent -- and does not appear to be using more than one core. On my laptop, Thunderbird has acceptable performance, and typically shows a load of 10 percent. Office LAN is IEEE 802.3 at 100 Mbit/sec; home is over IEEE 802.11 through a DSL box from the telephone common carrier. Anyone else having a similar experience? Is 64 bit Tbird significantly different from 32 bit Tbird? Yasha Karant