imap mailbox specifications that contain the "@" character in the username field causes the spec parsing to fail. This is due to the changes made in version 0.7.0 in order to get more flexibility in the password handling of imap mailboxes.
In versions before 0.7.0, the username substring was separated from the imap server substring by searching for an ":" in the specification. In version 0.7.0 this was replaced by the search for the "@" character, which causes the parser bug.
I don't know much about python, but performing a reverse split instead of a 'normal' split in line 1308 seems to work:
"imap_str.split('@', 1)" -> "imap_str.rsplit('@', 1)"
I believe this to be stable because the last "@" character always specifies the separator between user name and server as long as the imap server configuration does not make use of this character as the folder separator...