I do not think there is any way to disable that for that specific email client.
I do recommend K9 mail, however considering it is being mozilla'd, I might not recommend this client for much longer once Mozilla makes a mess of it.
I can't really help as I like to type all my emails on my Laptop, I hate typing emails on phone, and I only use it for reading emails, scanning barcodes which are emailed (for example for transit in the UK you get emailed your tickets), or if I MUST, I will reply to short emails.
This has got quite off topic, best to try to return to the original topic :)
Hope this helps.