Exchange not sending out attachments through cloudflare

I’m having trouble sending out email through an exchange server with attachments beyond 1.5MB via the MS Office Outlook app. Everything else about the exchange connection is functional! Outlook web interface also works flawlessly, even with the same outgoing attachments.

The same computer(s) will send out the attachments fine once connected to a different network (home, cell hotspot,etc). The on-site router has been eliminated from the equation by connecting a computer direct to the ISP’s Cisco.

The ISP claims no filtering is going on, and the next hop on a tracert is clouflare-ic-375749 ip twelve99-cust net. Does anyone know or suspect if this could be the culprit?

Welcome to the Cloudflare Community. :logodrop:

So that we can offer better answers, can you explain in detail for us where Cloudflare fits into this picture?

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They are the next router and they may be filtering exchange packets to fix a security hole, but it may be the culprit in blocking the outgoing email.

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