Email Quotas for Exchange
Email Attachment Limit for Hosted Exchange Email
The email attachment limit actually applies to the total email size, including all attachments. That limit is 100 MB and include one or more attachments plus the email content.
Outgoing message quota for Hosted Exchange Email
There is a limit of 1000 outgoing emails per Hosted Exchange Email account within a 24 hour period. Users reaching this limit will be scaled back to zero over a 24 hour period.