Retaining large files attached to a Skype for Business meeting
You can attach files to a Skype for Business meeting, which participants can then open and download. Files attached to Skype for Business meetings are retained in the mailboxes of any participant whose mailbox is placed on Litigation Hold, has a Microsoft 365 or Office 365 retention policy applied, or is placed on a hold associated with an eDiscovery case in the Microsoft 365 Compliance Center. This content is saved to participants' Recoverable Items folders in their mailboxes.
Files that are retained in mailboxes on hold are indexed and can therefore be searched when running a Content Search in the Security & Compliance Center when searching a participant's mailbox. However, attached files that are larger than 30 MB are split into two or more smaller files and saved as compressed (.zip) files. The content of these smaller files is not indexed for search and might not be returned in a Content Search. However, the metadata of these files (such as the file name and author) is indexed for search and might be returned in a Content Search.
The MaxReceiveSize and MaxSendSize settings for an Exchange Online mailbox can affect the ability to retain large files from Skype for Business meetings. The default settings for MaxReceiveSize and MaxSendSize are 36 MB and 35 MB, respectively. However, these default settings are too small to retain any file from a Skype for Business meeting that's larger than 30 MB. This is because Exchange Online uses Base64 encoding of message attachments and other binary data. When a message is encoded, its size is increased by approximately 33%. Therefore, to ensure that large files from Skype for Business meetings are retained, we recommend that you increase the value for both MaxReceiveSize and MaxSendSize to 39 MB (which is approximately 33% larger than the 30 MB size limit that was previously explained) for users who are placed on hold. Otherwise, a large file attached to a Skype for Business meeting might not be retained. For more information about using the Set-Mailbox -MaxReceiveSize and Set-Mailbox -MaxSendSize commands in Exchange Online PowerShell, see Set-Mailbox.
Mailboxes that are not on hold will not have any meeting data saved. For example, in a three-person meeting in which the mailboxes of two participants are marked for retention, the meeting data is saved to the mailboxes of those two participants, but not to the mailbox of the third participant, whose mailbox is not on hold.