Limitations with Office 365:

Office 365 Mailbox Staff Only

Mailbox storage limit50GB
Message size limit25MB
Attachment limitWith individual attachments limited to 25 MB
Subject length limit255 characters
Recipient rate limit10,000 recipients per day.
After the limit has been reached, messages can’t be sent from the mailbox until the number of recipients that were sent messages in the past 24 hours drops below the limit.
Recipient limit500 recipients, distribution group counted as one.
Message rate limit30 messages per minute
Retention period for items removed from the Deleted Items folder14 days
Maximum message size for large distribution groups (>5000 members)2 MB

Office 365 OneDrive

OneDrive (sharepoint included) storage1TB
Length of file nameUp to 128 characters
Length of folder nameUp to 250 characters
Length of file name combinations (including file and folder name) Up to 250 characters
File upload Limit2GB per file
Invalid file typesFiles with a *.tmp or *.ds_store extension, desktop.ini, thumbs.db, or ehthumbs.db (Full list of file type cannot be added)
Any file that’s currently open by an application.
Invalid characters in filename/folder \ / : * ? " < > | # { } % ~ &
No. of Items (files & folders) can be synced to OneDriveUp to 20,000 items

For more information, you can refer to the following links: