Every staff account in the remote hosted Exchange server has a hard quota of 50GB, but we strongly recommend you keep your mailbox much smaller than that. Exchange recognizes the size of your entire mail store, whether one or many email folders, and including deleted items and sent items.
Whenever you log on to Outlook at a new computer (eg at a different location, a new laptop, or an upgraded computer) Exchange will set out to re-synchronise the email database which will involve downloading the contents of your mailbox to the new system. For very large mailboxes this may take from tens of minutes to hours.
There are limits on the sizes of emails and attachments that can be processed by the Exchange mail service. The message size total is 30MB including the email and any attachments. The individual attachment file size limit is 26MB. The file size is considered "pre-compression" because the AntiVirus extracts all zipped files to scan them.