Hi Kayleigh,
According to my search, if you are receiving that when you send to another person, they will need to delete some of the mail in their mailbox.
Which means that there is a storage limit set on the recipient's mailbox, and it is currently full.
If the recipient is hosted in the same organization as you, the issue can be resolved either by:
- Deleting messages (deleting messages with large attachments via OWA or Outlook client)
- Increasing their mailbox limits.
If the recipient is hosted outside of your organization, contact the recipient directly and provide their mail administrator with the bounce back message.
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