I posted this as a comment to the Outlook.com blog, but I thought it would be good to bring this problem here as well.

The IMAP EXPUNGE command is quite slow for my account (and of my co-worker's).  I have a new Outlook.com account with 2 - 3 emails in it, so I don't think this is a scale problem.

It's easy to reproduce with OpenSSL from a console window:

$ openssl s_client -connect imap-mail.outlook.com:993 -crlf

Once connected (note, this will delete your oldest email in your Inbox):

a login <user> <pass>
[LOGIN responses]
a select Inbox
[SELECT responses]
a store 1 +flags (\Deleted)
[FETCH responses]
a expunge

At this point, with my account, the connection holds for 10s - 15s.  No other commands may be pipelined at this time.

This seems way too long for an Inbox of my size, with one message marked for deletion.

Note that the CLOSE command (which implies an EXPUNGE, but with no responses delivered to the client) also hangs for a similar amount of time.