@dbeato thanks for the link, I am aware of Gmail's attachment limit. But in this scenario, Outlook can simply override Gmail's attachment limit easily. And this is actually confirmed with G support.

What I don't understand is why it sends multiple copies.

An email is sent once but multiple Sent items appear at an interval of five minutes for as many as fourteen copies.

We noticed that this only happens when the email has an attachment of more than 24 MB (whether or not just one file)

In addition, Gmail should only allow a 25 MB email size (i.e. total file size of an email including body and attachment/s) but these emails go through and getting received by the recipient/s even for emails amounting to as much as 40 MB