Note: This process references the webmail portal for cloud users. If you are not a cloud user then use your organization's typical webmail link.
If you need to move a large amount of mail (entire folders) from a separate mailbox to yours or your archive webmail is the way to go. It can take a significant amount of time so doing it through the web will give it the appropriate time to move.
- Sign into webmail at outlook.office365.com
- Expand the mailbox you wish to copy from
- Right click the folder you intend to move and click "Move"
- Highlight the folder you want to move the folder to and then click "Move" to start the process
- Give it time! Moving a large amount of mail can take a considerable amount of time, it may appear it is not doing anything but it is slowly moving the mail over. When finished the mail will appear under the folder you moved it to.