@mattbarnes
In that case, if Google rejected to send your mails, you would receive sort of an error message sent to you by Google, that would (more or less cryptically) explain the reason for rejection.
Did you receive any related message? Maybe check your spam folder.
On the recipient's side, a common reason is that the storage is full. Depending on your opponent's mail provider there are sometimes ridiculously low storage capacities. Many users are totally unaware of these limitations.
Another reason might be that your opponent maybe plays on a company's PC, and the company's mail server set-up started to filter out those mails/attachments.
I doubt that a provider cares to reject *.tsvg files. But in the unlikely event a provider does, you can zip the *.tsvg to send out zip-files instead. Of course the opponent has to unzip the zip-file then, to use the *.tsvg file.
