Why do mail server care about how long a line is? Why don't they just let the client reading the mail worry about wrapping the lines?
The server needs to parse the message headers, so it can't be an opaque blob. If the client uses IMAP, the server needs to fully parse the message. The only alternative is POP3, where the client downloads all messages as blobs and you can only read your email from one location, which made sense in the year 2000 but not now when everyone has several devices.
POP can download the email, and that's about it.
Gmail basically is IMAP with a couple extras, and your desktop (via a browser) and your phone (via a dedicated app) can both see the same messages. Only the phone can work offline though, because there is little demand for a dedicated desktop email client, it's always via a browser. But Google could easily make such a thing if they wanted.