[Users] IMAP and attachments

[Micha]

I have to admit i don't know how IMAP deals with attachments. 

Let's say i save a draft with huge attachment, then is it also saved to some local cache too ? So that if i'm going to work on it again another day, i don't need to download the attachments again ?
 
But isn't that contradicting the idea of IMAP, when i could have modified the draft meanwhile from another machine, so it really needs ot be downloaded again ?

But can i configure or chose that behavior somehow ? Because i'm often on the road with rather low mobile bandwidth.

For example, i tried this:

With IMAP, i configured claws drafts to be saved in a local folder, instead of the IMAP mailbox, because of the the auto-save behavior. Let's say, i'm working on a draft and attach some huge files (which i do very often; 'huge' is 10 - 30M for me). Then at some point, that draft is saved automagically, and the slow upload of the attachments blocks me from going on with the mail work.
(There are some more things or cases when mails basically could be saved local, too.)

Is that an advised way of doing things, or could someone please enlighten me how to avoid my problems in the first place. is IMAP simply not meant or equipped for low bandwidth conditions ?