Its late.. I need some sleep.. so just a few words:
Have fun with it. 
Mail2Blog Extension v0.1 - 21. June 2008
As every extension it’s released under the Ms-PL
For usage informations, installation notes and so on, take a look into the readme.txt in the zip file…
Later I will create a page for the extension, where I’ll put those informations too, but now I have to go to bed.
Oh.. and.. I have used this extension several times on this blog and it worked without problems, but the released one is a little bit pimped up.. So there could be some bugs, or other crazy things. Please inform me about weird behaviour. 
Mhm.. and you need a current version of BlogEngine.net (at least with this extensionmanager thing..) and it would be fine when you’re able to do some changes to the code of BlogEngine.net. (Reason is explained in the readme file, and here is some explanation too )
And now.. good night.
whoops..I forgot to mention how to write an email to your blog:
Just write a normal email to the configured email address, but some special information in the subject:
[BLOG] *these are tags* #these are categories# ‘i am the author’ “this is the subject of the posting”
The [BLOG] part is needed, but can be configured to some other text. (Called prefix on the configure page)
Then you have a tag and a category list. You can specify the author, and the subject. These infos are recognized by the characters surrounding the information.
So remember:
* -> surrounds tags
# -> surrounds categories
’ -> surrounds the author name
” -> surrounds the title
None of them are required infos, except the prefix part. ([BLOG] in the example above..)
Update 3. July 2008:
Here is the patched core dll to use with the mail2blog extension. It’s the code from the official 1.4 release but with the 2 modifications needed.