Using New Outlook on Windows for professional communication and productivity
Hello @Ali E
Since your mailbox is capped at 55 MB, your IT team has already increased it above the default. Whether it can be raised further depends on your organization's Exchange settings and policies. Exchange Online supports up to 150 MB if the admin chooses to allow it
You can find more information about Exchange Online limit via here.
As these settings are managed by your organization's Exchange administrator, individual users cannot increase the limit themselves. We recommend contacting your IT administrator to verify the configured maximum message size for your mailbox and determine whether it can be increased based on your organization's policies.
If you're unsure who your IT administrator is, please reach out to the person or organization that originally provided your Microsoft 365 account, as they should be able to direct you to the appropriate contact.
We look forward to your reply.