My understanding is that this is not a matter of discrimination against Mac users. The increase can be made in one of 2 ways:
- Admin action in an Exchange/business server environment.I believe Mac clients should have the same benefit
- Local increase by way of a Registry hack, but there is no registry access supported by macOS
Either way, the sender's service may have no limit but the service of virtually all recipients is restricted — although informal, 20mb is a rather universal standard. An oversize attachment may send OK but still will result in a bounce-back or be stripped.
Have you considered the recommended method of saving to a cloud & including a share in in the email message?