Currently the input field is grow up to 3 lines in android client and only 1 line in desktop client while typing.
It would be easier to see more text while I type a longer messages.
Since the input field is automaticly grow up it would not hurt if I write a “one line message”. But if I write a longer message (closer to Email the to short message) I would see what I have written.
So I would prefer a larger input field up to 5 lines or more (espacially desktop client)
or perhaps a more flexible way, that allow to expand the “TextArea” while you are typing a long message something like a compositing view that you can toggle by double tapping the textview.
I have to say that I had bad experiences writing messages longer than 3 lines
That’s what I mean.
not really, I am talking of a (maybe full-screen) view for writing messages that users can toggle with the default 3 lines mode
OK, I got it.
But let’s say 5 lines 
For me it sounds like a good idea.
Especially Deltachat is still a “Mail client” and I write also sometimes mails, not only short messages.
That’s why I want “new line” by pressing the Enter key for desktop client.
Agree in that, Delta Chat must be good a enough so people doesn’t need to use another mail client!!!
Other wise it will be not as good as a chatting app and not as good as an email client, at least Delta Chat must beat email clients, so if users don’t replace their chatting app with Delta Chat, at least they still use Delta Chat as a better email client!!
Let’s say DeltaChat is a hybrid between messenger an mail client.
And with a good design it can replace mail an messenger 
But if it’s in the main a messenger it’s great.
For official mails I still need a normal mail client with:
-subject line
-to,cc and bcc field
-quote of the replayd mail
-more attachments in one mail.
And so on.
And this would overload DeltaChat
I have seen “Delta Chat”-like apps that include all the “conventional email client” functionality in the DC equivalent of “Contact Requests” view, but right now this is too much for DC as you say…
Desktop only
(or mabye as of Tablets: all versions)
I suggest a resizeable composer/viewer window (default eg. 79chars width)
or to say a pop-up window for writing and reading for the bigger emails.
E.g a reader icon in the chat bubble.
clicking on it - a window pops up for reading it
Mabye with a backward and forward button (for e.g. attachments)
Maybe also a search button.
E.g a writer icon in the input field.
clicking on it - a window pops up for writing/continue a new message.
This module could get a spell-checker (+maybe formatter, style) onetime.
Clicking “Send” closes the window and goes the normal flow then:
a new chat bubble.
Or
maybe easier a “Ready” button:
which simply copies it back to the input field to proceed.
And maybe onetime:
For to, cc, bcc I would suggest:
Each contact is already available as chat or group chat.
So you can choose from available chats.
So its then “simply” copied into each chat.
[where to “To,CC,BCC” is copied on top of the message accordingly
as Invite-To-Chat Links or maybe Invite-QR-gifs (e.g. as attachments)]
I think such a “hooked” module could leave the core nearly untouched
yet extends the functionality/usability for the bigger emails.