Update:
I've just done some tests and it's not that simple.
If viewing an image (in Gallery or some image prog like Photobook) and you select Send / Email and try to email that image, the size limit seems to be about 500kbytes i.e. almost totally useless.
And it's got worse. The early Belle (N700 phone) could email 3-4 images fairly reliably i.e. a few MB. Not any more.
However I have just done a movie, 21MB. I emailed it to myself, by creating a new email inside the email app and then attaching the .mp4 file to it as an attachment.
That emailed fine!
The emailed size (uuencoded or mime encoded; can't easily tell which because this email app has no config options for this) was 40MB!
That's a massive email which most people would not be able to send (or receive) due to SMTP or POP server limits.
But it worked.
The only bug I found (and THIS IS A VERY SERIOUS BUG) was that it appeared un-sent i.e. was stuck in Outbox. I deleted it from Outbox; so far so good.
But then I found that my free space on c: dropped by about 40MB.
So, using ActiveFile and this being a jailbroken phone, I was able to go to
c:\private\1000484b\Mail2\00001001_S\4\001026d4_F
and in there I would the huge .mp4 file and deleted it.
While in that 1000484b directory (which is where Belle stores emails), I found dozens of orphaned .jpg files, and my c: free space increased by 50MB by deleting those.
Looking at the dates on those files, many and possibly all of them were ones where I was emailing from the Gallery and the emails crashed the email app, dumping the email in Drafts. However it appears that sending those emails (from Drafts) leaves them orphaned in the filing system.
NOKIA NEED TO FIX THIS. NO WONDER SO MANY PEOPLE HAVE LOW C: SPACE.
The above is with the latest Belle update, downloaded yesterday.