Using multiple From: addresses and recognizing mails sent to them as sent to us has been requested recently:
Here the problem of multiple chat for the same sender is caused by Delta Chat creating a new chat with 3 members (itself, an alias, and the sender contact) for each mail received with an alias in the To: field:
A simple solution is to allow to configure multiple “self” addresses and mark one of them as primary used for sending. The problem I see here is that if someone adds your alias address to some chat, other members will not recognize you as a member when you send a message there from your primary address.
To solve this Delta Chat needs to have multiple “self” contacts, so you can participate in different chats as different aliases. This also means that for each contact you can have multiple 1:1 chats and can participate in some group as two different aliases. All of this has to be presented in the UI somehow.