Just curious, since Spamsieve is only 32-bit, should Mail be 32-bit also?
SpamSieve’s Mail plug-in is both 32-bit and 64-bit, so you can run Mail whichever way you want. 64-bit is probably a little faster, but it likely uses more RAM.
Does the fact that Spamsieve itself is 32-bit make a difference?
No, that doesn’t matter.