@Fabianb: Yes, you are right, you then cannot assign the eMails to workspaces, but you possibly could store the eMail-Account-Information and perhaps make a relationship (i.e. link) to an eMail stored in a remote imap
@Winchester: Yes, thats the idea. I for myself currently use squirrelmail, but I feel also comfortable with roundcube. Possibly the implemented library swiftmailer
http://swiftmailer.org can be used to query imap...
I for myself would find it very usedful to have this possibility, because normally every environment has already an eMail-System before using or migration to opengoo...
Thomas