No problems here after the last Windows-Update (2 days ago) (and no idea about the relationship with SuRun). Most probably you got the latest Patch via Auto-Update and that has nothing to do with SuRun.
But ...
Noobody wrote:And Windows Update appears to run fine in the SuRun account using limited rights. But of course, I can't download updates.
This appears as a contradiction and I don't think, that your first sentence is valid. Probably you should rephrase that for expressing, what you want to say.
If I understand you correctly, the DCOM-error appears regardless of starting the mail-client (why don't you say, which one) with (not a good idea to run a mail-client elevated) or without SuRun; so this problem is somewhere else.