PS - Exchange Online Mail Limits

The default send and receive message size limit within Exchange Online is 35MB, to amend this (currently to a maximum of 150MB), use the following commands:

To modify the MailBoxPlan for all future mailboxes:
Get-MailboxPlan | Set-MailboxPlan -MaxSendSize 50MB -MaxReceiveSize 50MB

Modify an individual mailbox:
Set-Mailbox -Identity -MaxSendSize 50MB -MaxReceiveSize 50MB 

Modify all existing mailboxes:
Get-Mailbox | Set-Mailbox -MaxSendSize 50MB -MaxReceiveSize 50MB