I dunno, there's something about email that makes a lot of people write more thoughtful and comprehensive messages. Not everyone, obviously. But it feels more like writing a letter - you're not expecting a reply within minutes.

You're right but thats because of the social rules around email. With instant messaging people are very used to casually using it in their day to day life so you're fighting against that. But I still think its worth doing

It might be partly social rules but I think a lot is down to UI/UX and the underlying protocol. Email clients by and large look very different to chat clients. When you draft a new email you're given a bit white space that expands easily as your message grows, rather than (at least on phones) a tiny box that conceals all but the last few lines. There are prominent options about whether to reply, reply-all, or to cc further recipients. You can even bcc people. It's normal to have multiple separate mail threads with someone, rather than a chat window that contains every message you've ever sent. You typically send emails to an address, but you send IMs to an account. Companies will email you with periodic newsletters, sometimes unasked for. And so on!