Only messages under 10 MB come through — does POPcon impose a size limit?

POPcon itself handles messages up to 100 MB and beyond — there is no practical size limit in POPcon. The 10 MB restriction is coming from Exchange.

Exchange enforces message size limits in three separate locations — all three must be increased:

1. Receive connector: Server Configuration > Hub Transport > Receive Connectors > default connector > Maximum message size
2. Organisation-level: Organization Configuration > Hub Transport > Global Settings > Transport Settings > Maximum receive size
3. Per-mailbox: Each user's mailbox delivery restrictions in Active Directory Users and Computers

Use the Exchange Management Shell shortcut: set-receiveconnector "*default*" -maxmessagesize 100MB

Screenshots — step by step