In the upcoming migration from Zimbra to Office 365, email messages with attachments greater than 25MB will not migrate. Both the email content as well as the attachment will not be moved to Office 365.
For emails that have attachments larger than 25MB, it is recommended that you download any attachments to your computer that you will want to keep, as they will not migrate to Office 365. See the Knowledge Base article How to identify and download mail attachments larger than 25MB.
Settings on Zimbra have been adjusted to reflect the 25MB attachment limit on Office 365; previously Zimbra had been set to accept and send emails up to 50MB in size. Beginning immediately, you will not be able to send or receive any K-State email that is larger than 25MB. All email already in your Zimbra mailbox will not be affected by this change.