Is it possible to increase send or receive size limits?

Yes, it is possible to increase message send/receive limits.

We will customize your shared plan or recommend a more advanced option depending on your needs.
There will be additional costs and we cannot impact our other shared hosting customers, which is where the advanced option comes in (such as your own managed e-mail server).

It’s important to keep in mind most businesses offer support at or around 15 MB even though there isn’t an industry standard.
Once you begin sending messages above 20 MB, it’s highly possible businesses will reject these messages due to size restrictions in place.