Internally there is no maximum attachment file size. However, emailing large files is inefficient and eats up allocated email storage space. It is encouraged to use other means of transferring large files (e.g. network share, external USB key or drive, dropbox, etc.).
Employee email maximum size set at mail gateway: 112 MB
Student email maximum size set at mail gateway: 112 MB
Keep in mind that when you send a file as an attachment, the file will be encoded in the text, which will generally increase the file size inside the email message. This will vary based on the type of file being encoded. Therefore it is best to keep attachments under 35 MB for both Employee and Student.
The receiving email gateway/server may have its own inbound maximum file sizes set, so there could be cases where although the email may have been under the maximum file size on the UFV end, it is rejected on the receiver end.