User can’t send zipped ppt email outside of network

Sgt Schulz sent this response:

‘as for copy of undeliverable report and exact email addresses with problem.
how big is this file? might be hitting attachment size restriction.
also, everybody is quickly reacting to new virus infested zip files. filtering them out of company emails. perhaps you are seeing that. try resending yourself with the zip file renamed file.zix. have recepient rename it back to file.zip when received”

Whats the procedure for renaming it?