You both did reboot the postfix docker container, e.g. by doing
docker compose restart postfix-mailcow ?
Also, you can enlarge the setting in mailcow, but it is highly doubtable if the receiver will accept such large attachments. e.g. this is from gmail:
Attachment size limit
The Gmail attachment size limit for incoming emails is 50 MB. That means you can accept emails from other people of up to 50 MB.
You can send up to 25 MB in attachments. If you have more than one attachment, they can’t add up to more than 25 MB.